I believe this is a small bug/ annoying thing that should be fixed. Its not a very big deal tho 
As shown in the attached screenshot, the circle hitbox for a bombard cannon is inaccurate - the front part of the cannon is excluded and there is a bit of area at the back of the guy (empty space) that is actually inside the hitbox (marked by red arrows). This means, if a cannon is hit only on the front edge it actually doesn’t take damage/full damage where as if the cannon lands in the empty space behind, it still takes full/significant damage. This is not a big deal really in normal games, but when doing bbc vs bbc micro with “Attack Target” because you target the front side and it isn’t affected when hit.
(Btw, I only noticed this when playing Dodgeball bbc scenario a lot in the past few days 11).