When do you stop cubing for boss %?

consider %boss to be a countermeasure for damage reduction bosses (like Hilla) 100% bossing, will counter her 50% damage reduction.
this is separate from, but similar to, ignore defense and PDR relationship.

Just to be picky, 100% boss does not quite double your damage, because it is not a straight multiplier even though you would think it should be.
See Joe Tang's % damage tables to see what I mean.