If you've lifted like a powerlifter, you may get virtually no upper pec activation from inclines, or pec activation from benches at all.
I'm not joking, my pecs don't even tense benching with a powerlifting set-up.
I do have big pecs though. The size came from dumbell presses at different angles. Even here, I can't go too heavy. If I pound out reps with 115 pound DBs, I get little pec involvement. If I drop down to 70s and focus on FLEXING THE PECS, and just using the bells as tools to produce tension, then my pecs pump up like crazy.
See, I think you should almost be shrugging the pecs at the top, which is the exact opposite of what you want to do for powerlifting.
For inclines, I lower the dumbells NOT straight elbows out, but elbows somewhat out and arching down a little toward the feet and out, almost like a flye. This is with a slight incline. At the top, first the weight should not be straight over your shoulders, but a little in the inferior direction, then squeeze the pecs to bring them over the shoulders.
One interesting thing though. Military presses from the front DO get the upper pecs somewhat for me very independent of the lower head.