I posted this to the Steam forums, and it went down well there, but the devs didn’t pick up on it for whatever reason.
I’ll repost it here –
Unspent AP should be subtracted from Fatigue at the rate of 1:1. (meaning if you do not take any actions in a brother’s turn, you regain 24 fatigue as opposed to the usual 15). This would make “Tactical” turn choices such as only using half your AP or tactical positioning more interesting and it would also mean you could rest brothers off turn if you wanted to regain fatigue in a hurry.
1:1 isn’t going to break anything, but provides a nice little fillip to things, and should add a little extra tactical depth to proceedings.