So, for some strange reason I'm a big fan of creating old-school bruisers in MyCareer. I'm talking Shaq-style guys that set screens, rebound, block shots and dunk when open. In 2K14, it was great, I could do all of this and had no issue dunking off offensive rebounds and off the pick and roll or just in general being open within 5 or so feet of the hoop and just going up for the dunk.
Something happened with 2K15... although I was 7'2" with major wingspan and maxed out Athletic skills, I could only do dunks with a 2-3 step head-start when using the shot-stick. I later found that, for some reason using the Shot Button WOULD allow me to dunk from anywhere.
This year I started with similar MyCareer, but only a 6'11" guy. Had a promising start in both High School and College where he dunked with no issue from within 5 or-so feet of the rim. THEN in the NBA, it all changed. In MyCareer, I dunked for the first time today - about 12 games into my second season (I'd been playing HOF and set it to ROOKIE just to try to dunk). Even then, it only came with a 3-4 step running start.
It's kinda ridiculous seeing my guy open under the hoop off a pick and roll or offensive rebound and just throw up a reverse layup (which of course he has a low attribute score for) instead of going straight up just a two-hand dunk. I've just screen-recorded both that game and in just a few minutes of MyCareer's shootaround showing that it's impossible to do a standing dunk. Will upload to YouTube and post a link shortly.