this may not be a popular opinion, but i doubt it has much to do with your training...you're probably a big boy, and have been lifting for some time...i'd be willing to chalk this one up to genetics...
take two different guys, about the same size, give 'em the same sauce and the same routine/diet...it's doubtful that they'll develop identically...
my partner trains just as intensely as i do, and on the scale he's close to my weight, probably close to my bf%, but that poor bastard just can't do shit on a flat bench...not sure why, his arms and chest look about as big as mine...
i could easily stand corrected, this is just my opinion...btw, changing your routine and adding drops sets, etc. is a good way to break past plateaus...just wanted to agree
AM