Some thoughts on replacements

[case23]

Between scenarios
Elite cost 5% of the purchase price per strength point
Green replacements are free
Overstrength replacements cost 10% of the purchase price per point

In a scenario
Elite replacements cost 10% of the purchase price per strength point
Green replacements cost 2.5% of the purchase price per strength point
Overstrength replacements cost 20% of the purchase price per strength point

It takes a unit's full turn to be brought back to full strength (depending of course on limitations from enemy units next to it). It then takes another full turn to add one overstrength replacement.

Green replacements appear to remove approximately 1/14 of the units xp per strength point of replacement. One point would remove 1/14 of xp, four points would remove 4/14 of xp, etc. This is true regardless of whether done in the scenario or between scenarios.

Observations and opinions
Warning: I haven't even beaten the game on iron man/FM (can't get through US East... yet), so my opinions may well be ill-informed. Also, I only play IM FM, so my thoughts are heavily slanted towards it. Nonetheless, for what they might be worth...

You should probably have a very good reason to add overstrength points in a scenario.

If you will spend the points for elite replacements for a particular unit in a scenario, you should probably add overstrength points between scenarios -- the cost is exactly the same.

It causes very slightly less xp loss to replace losses as they occur rather than waiting for the unit to be significantly damaged. For example, a 400 xp unit will have around 275 xp left after taking one strength point of damage five times and being brought up to full strength after each time. If the unit is brought to full strength only after it has lost all five points, it'll have around 255. As you can see, the effect is so slight that it's probably not worth considering.

Since xp loss for green replacements increases as xp increase, elite replacements become more cost effective (in terms of cost per xp saved) for more experienced units. Put another way, green replacements hurt experienced units more than they hurt inexperienced units, but costs are the same in both cases.

When evaluating green vs. elite replacements within a scenario, I generally roughly estimate how many xp I'm saving per prestige point as one factor (there are other factors that might be more important, of course). For example:
Pionere + SdKfz 251 purchase cost 293
Green replacements 7.325/point
Elite replacements 29.3/point (21.975/point more than green).
If it has 280 xp, I'll lose around 20 points per green replacement point, so it's a bit more than 1 prestige point per xp saved to use elites (21.975 prestige / 20 xp). I would probably use elites in this case. (Warning, that may be stupid -- I'm not giving advice either way on what to do, just pointing out one possible factor in the decision.)

Evaluating cost/xp has the flaw that higher cost units naturally have a higher cost per xp, but higher cost units probably are also more effective, making their xp more valuable. It might be better to evaluate the cost-normalized prestige cost per xp, which amounts to simply considering the total xp saved. To add even more nuance, one could consider that xp for units that ore often overstrength (air assets, artillery) might be worth spending a bit more prestige on. It's possible that level of analysis is overkill .

I routinely overstrength all units before scenarios. I think having the extra punch in the first couple of turns is worth the additional cost. Furthermore, it's equivalent to buying elite replacements rather than green replacements in the scenario for those strength points, and the cost difference (over using green replacements in the scenario) amounts to 7.5% of the purchase price per point.

I'm currently experimenting with using elite replacements in a scenario as long as I'm not spending more than 2 prestige per xp, with exceptions for artillery and tac bombers (always elite, though I've probably screwed up if a either one needs much in the way of replacements) and fighters (generally don't replace in a scenario because in vanilla once I've achieved air supremacy, they're typically are used for entrenchment reduction, scouting, and occasionally attempting to pick off the not-quite-dead unit). I use elites between scenarios always unless the xp loss is trivial (10 - 20 points, say).

Comments, thoughts, and disagreements welcome.

- Case

[dumbttt]

I generally use elite replacement and always overstrength between scenarios. I try as much as I can to not use any replacement in a scenario. If I must, I generally use green if it doesn't hurt my unit too much. Elite replacement in scenario will cost a fortune.

[Wiber]

Excellent analysis Case23 My own use of replacements is the same as yours - IE I over-strength /elite replace between scenarios and do a cost benefit analysis during the scenario. My simple rule is look at the tool tip cost analysis. If it won't drop them below a star point thresh-hold I will green replace them. This lasts up to 200xp. After that everything is elite.

Wiber

[FOARP]

I always use elite replacements with core units, always over-strength between scenarios if I can afford it, and will normally use eleite replacements as a way of resupplying if I can afford it. I never use elite replacements with non-core units except by accident.

The way I figure, my units will become elite much faster if I don't cut into their experience early by using green replacements. Some untis will always end up taking heavy loses in a scenario, and if you green-replace them, you're just taking that unit back to square zero.

[GSlapshot]

I concur on not using elite replacements during a scenario. Also don't let a unit get too damaged since the green replacements lower experience drastically if the unit strength is below 6. Also in the GC's you gain experience quickly so you can easily get it back in a scenario with successful combat. Also note that it is the number of "kills" that reward you with a hero not experience.

[case23]

I'm guessing there's a significant difference in the optimal replacement policy in the DLC and the optimal replacement policy in vanilla. While I can't quite go whole hog and make every replacement elite, I'm convinced I don't have to go all green. Also, of course, FM puts a premium on experience since it's slow to get. I might try that on my next run through -- only green replacements in the scenarios. My sense is that I'll have too much prestige, not enough xp, but I might be wrong.

In DLC, where there's an xp cap, green replacements make a lot more sense, since you can in fact get back the xp you lost (the xp cap presumably means that you'll occasionally lose xp by being at the cap in any case). In vanilla, that's not the case. Lose some xp, and they're gone forever. You can earn more, but you'll always have less than if you hadn't lost any. (This assumes that the rate of xp gain doesn't slow as you get more xp. If it does slow, the xp cost of green replacements is somewhat mitigated by the increased earning rate.)

I think one of the things that makes the game so interesting is that there are some great optimization problems around and alongside the tactical challenges. The three-way dance of prestige, xp, and mission objectives interact in very interesting ways.

- Case

[Horst]

Using green replacements during battles makes sense if you already hit the cap in the DLCs. I should do this too now because units like Tigers eat prestige like T-34 for breakfast. I’ve already lost like 7k prestige because I thought it is cool to pass the Don River in Belgorod 43.
I used Tigers only later in Africa until the end but prestige also got very short in the end, in particular against those pesky Fireflies.
In DLC’s, I've adopted now in 43 the same historical formation to use Pz IIIN to deal with infantry and will only have heavy tanks in my SE spearhead. The other two spearheads have “only” Panthers at moment with all three supported by one Elefant, but I’m afraid even this is getting too expensive with my sloppy tactical ability. I really miss these Stalingrad city maps with the many flags to rake prestige in. It's getting more wise to avoid enemy contact and seek only the victory hexes unlike in early war when grabbing all flags was kinda mandatory.

[Longasc]

Maybe I should bring some units to overstrength, I am usually struggling with prestige on FM. But maybe it's worth it, many seem to routinely spend lots of prestige on that.
Bad things happen if you don't play the save/reload game and it costs a lot of prestige to replace the losses. So I usually don't feel I have the necessary prestige reserve to overstrengthen units.

[case23]

I've seen opinions in this forum suggesting that at least putting air assets and artillery assets overstrength is worthwhile. I think that makes a lot of sense. You're more likely to get the benefits for longer since they're often not getting shot back at and the extra dice when attacking really add up. I find making infantry units overstrength to be pretty cheap (29 prestige per point for pionere with SdKfz 251, which is my default infantry past the low countries in vanilla.

- Case