Slitherine

I know that on FM level your units have a penalty to experience gain. Does this penalty applies to the extra three levels? After playing on FM, on Rommel the units seems to gain experience faster.

The bonus difficulties do not have a penalty to experience. You can adjust this yourself by going into gamerules.pzdat and halving all the expgrowth rates.

Thanks!

Could be that Field Marshal level is more difficult than Rommel? Since with the faster experience gain you can use most of the time green replacements diluting the experience but still having one or two stars, while on FM unless you use elite replacements on a regular base, your units will be most of the time almost inexperienced. Also, the new units will have a harder time to catch up with the rest.

I think Rommel is harder. -50% prestige is significant. You will end up with more experienced units on FM, as long as you use elite reinforcements, which you can afford without too much of an issue.