Ever consider pre-exhaustion technique for delts? IT really brought out the roundness and separation in my shoulders (pretty lean already). Do the isolation moves first such as side laterals, front raises, etc.. A great substitution sometimes for a phenominal burn is side cable laterals with a d ring from behind the back instesd of from the side with dumbells. Pause a couple inches form the top and then complete the motion. Pyramid up and then down in weight. After all the isolation moves are complete, when you do the presses the assisting muscles ( triceps, etc.) can"t take so much stress off the deltoids because they're semi burnt. Try this and see how your delts feel after a day or so. Also, I prefer to do rear delts and traps with back.