108 Bocce doesnt gain bonus damage no matter how high the difference between Luck and Curse is.
I read it on the Wiki that it should get stronger the more luck or curse you get. Either the wiki is lying or it is bugged for Xbox one. Or the bonus is so small that it isnt noticeable unless the difference is 10000%. This weapon is really weak without this gimmick and not worth using as long as this (maybe) bug Exist.