Just because you're creating a global arch with the bench press, doesn't mean that the rules change for the breathing and bracing mechanics. It's going to feel a little bit different because you're not in that completely stacked position. However, when you're set up in your optimal global arch, the trunk still doesn't move, we shouldn't be seeing differences in spinal position in the mid-movement, and for the reason of trunk stability, the rules around breathing and bracing still apply.