Slitherine

First, I like Field Fortifications and think they should be a thing on the Renaissance battlefield, as they were historically.
They are a bit hard to come to grips with as info regarding FF are spread out in the rules/errata though. I understand everything up to the point when they are assaulted (the enemy having to stop just before so they can be shot up a bit is good), but then it becomes a mess. I'll just write down things that I think I understand and may have issues with.

The way I understand it, they are not to be considered as any form of difficult terrain, but any POA demanding open terrain is void. But they do not cause any disorder and the Attacker is not considered to be in a state of DISORDER. Correct?

Any infantry defending them becomes "protected" (like protected pike/shot), as far as I can see in the errata. That means that several POA is cancelled against FF. Seems fine.

Cavalry cannot defend FF (?). But FF can be charged by cavalry? Really? How is that even possible? I'd think it is a bit strange even that cavalry can ride across FF (if they are unmanned).

The only things that get +POA against them during Impact is Impact Foot, Elephants (seems ok) and Foot using Salvo (a bit strange since the target is in cover...).

In Melee, Elephants and Better armour get +1POA. Pistol, Swordsmen get +1POA against the defenders if they are not STEADY which seems fine. But then there is this: Pike in 4+ ranks get +1POA in Melee. What?!? I could just about accept if the defender could get that (should they have Pikes) since they are standing still, but the attacker? How do you do a push of Pike across fortifications?

FF give +1 POA against anything. Good, but should'nt that be "final overall POA" as long as they are steady, or something to that effect?

Regarding the discussion about firing arc for artillery behind FF I think they should have a greater arc, if they cannot pivot, by the way. Pivoting but keeping a edge of the base in contact seems an easier solution, but I see why that could be a problem.

From the roar of attention I gather this is not a prioritized area of the rules. But could someone with experience just explain if I got the rules right concerning cavalry charging FF and pikes in 4 ranks getting POA in melee? And if so, why is this so?

I'm no expert but:

Having rules about crossing undefended FF was thought an un-necessary complication.

Mounted can charge FF but not recommended.

Pike cannot be used in 4 ranks whilst attacking or defending FF as FF are not counted as open terrain which would give you the POA. Same applies to any other POA derived from open terrain usage.

If I'm reading it correctly, Open Terrain is not a requirement for getting Pike-POA in Melee, only in Impact.

Sorry, I should have said Impact. Once in melee, assuming everything else is equal, defenders will be up a POA.

That is not what it says in the basic rules. Under Melee, it says pike in 4+ ranks get +1 POA if not fragmented or severely disordered. Nothing about terrain or FF. I'd love it if I am misreading this or if I've missed something. Please enlighten me.

When I said all other things being equal I was envisaging two identical pike blocks fighting across FF so in melee they both get a +POA for four ranks if they have them. Foot defending FF get a +POA hence defenders one up.

Obviously if the defenders get no +POA for any other reason then it will be evens.

Told you I was no expert

No problem. Guess there will be house rules about this, no way I'll let pikes get +1 fighting over obstacles.