[Suhiir]

All this leads me to wonder if FAE ammo in general is "properly" rated in game.

Without going into a lot of details (in this post) in general FAE's are not all that effective in open areas, i.e. outdoors. This is one reason no one has bothered to make FAE artillery rounds for instance.
FAEs are VERY effective in enclosed spaces, why they're used as bunker busters.
Since there's no way I'm aware of for WinSPMBT to determine if a given target is a building vice in the open its probable that in-game FAE effects for enclosed targets are being applied to targets in the open. Making FAEs a lot more lethal then they should be vs most targets.

So the question is...do FAEs get under-rated vs the (limited number) of target types they're very effective against? Or over-rated vs the (much larger number) target types they're of more limited effect on?

If desired we can discuss the precise characteristics of FAE...but I'm not sure anyone is THAT interested in Physics 101.