It seems to me that if you have 2 engineers in a battle, they should recover 100% of the drills. (each provide a 25% recovering + an additional 25% when in combat = 100%)

I have a situation with 2 engineers, but they are recovering less than 100%, possibly due to rounding issues because though simultaneous, their abilities are calculated and rounded individually?

i just looked at your game and it seems fine. you have 207 drillers before and 207 drillers after. is that not what you're seeing?

Sometimes they recovered 100%, other times less a few drills. at least, they did in the time machine. There may have been a difference in actual combat, I wasn't pay too close attention since in that situation the losses were not important.