How exactly does holy symbol work now (Post bb)

HS always gives 150% of the exp. It's just that the maximum exp you can get from a monster is capped at a certain value which depends on the number of members in your party.

For 1 person the exp is capped at 110% of the monster's exp, for two I think it's at 121% or something of the likes.

That wouldn't hold true if it were determined by such a requirement, for skills such as dice 6 and taunt would not give their full exp boost.