So... did some testing and combined is beyond anything anyone has understood. The way it works is as follows: It finds the highest damage modifier possible, then the lowest possible (if multiple armor types are present) and then average the 2 of them. So for flamethrower, against an armored bio unit, will take 8 + ((5 -3)/2) = 9 damage. This also means most weapons are totally off in terms of actual damage. Ironically this means that the flamer is LESS effective against light bio then pure bio, since light bio will get 8 + ((2+5)/2) = 11.5 damage.