Last time someone posted a question about isolating specific parts of the chest on the training board, it went on for 6 or so pages and ended up pretty nasty at times
lol i remember that. in my experience, you CAN target upper lower (emphasis) but i havent had any luck with inner, outer. i think its mostly genetic, i know i guy that does wide grip presses only and he has the sickest mid-chest seperation ive ever seen.