Actually the AI is pretty stupid right now, and _doesn't_ seem to respond to strength the previous turn. One of my MP games, Pythium's player went AI real early - I've kept the same army, with the same 31 PD, in the same province, and chewed up 3 attacks from Pythium's best troops. Things like 70 troops attacked, 56 dead, 0 friendly casualties (because the PD kept things from getting near my elite, armored, demonic, longbow samuraiwomen).
This happened three times in a row in one province (I'm staying there partly because I have a temple built), while a second province also slaughtered 2 attacks, lost to the third because I moved my demon archers out to cut off an army / province.