pile of crap, i think they just decided "lets make it seem like they are evenly matched, then have the enemy send in a sht load of stuff that makes no sense manawise!" Its like that cell game, where it says "difficulty gradient" or something like that, and actually just puts the game more in the opponent's favor entirely. Complete and utter bull. -1000/5 (idrc if i get -s, go to hell game)
As far as i know, it isn't possible to remove the dead zombies' corpses ingame. However, there is a way. Simply refresh the screen. Of course, this brings you back to your last save. Therefore, it is best to go to the next day as a save mechanism, then refresh to have a clean map. More zombie fun :3