yes, in theory. BG2 was said (in the promo-time) to apply the STR-bonus after multipliing but these high backstabs wouldn't be possible with the STR excluded. Without any potions or criticals I never had backstabs under 60, mostly 75-90, some times more.
In BG1 the STR-bonus was multiplied, I'm sure about that. Bioware wanted to alter this but didn't touched it for some reason.
btw. a funny thing: The whole German version of D&D 2nd edition is buggy, because according to the rulebook (which I have right before me), STR-boni are applied before multipliing. Played this many years, even on Game conventions.