Bench press: Actually with the ankles crossed and the knees up you will be allowing more strict attention to the targeted muscle area, that being the pecs. Somewhat confused as to why more tension (rather than pressure....we don't want pressure) would be directed to the anterior delts rather than to the pec's (major and minor) in that position. Hand gripping will dominate the influence of either the pec's themselves, the anterior delts or even the triceps.. When arching the lower back to the extreme and pressing the legs/toes from the floor, a lot of that direct tension is lost. That is a PL'ers style, not a pure BB'ers style.
Decline press: This has been a rewarding movement for some, with DB's usually the choice for experience BB'ers. But for most, it can be annoying just to get into the position without a good spotter and does not always reap the results wanted. Truth be told, some just do not like the feeling of the exercise with the head in that lower position. Personal view only.....is that dips (weighted) can be a more result producing experience than decline presses (or even flat bench presses), recruiting the whole upper body, including the ab's strongly. And a more effective movement , taking the TUT (time under tension) into consideration on the whole of the chest structure (major/minor pec's) . Weighted dip's referred to here.
Just to note, if keeping the body at a 180 degree angle when dipping (have a training partner hold the feet/lower body or brace the lower body/feet against a bench or whatever) than you have a superior tricep builders. Might also suggest using a "V" bar when dipping, if your gym has one. Allows different hand gripping, going from narrow to wide. Like the bench, trying different grip positions can make all the difference in the world when seeking development and strength. Dips are one of my favorite exercises. I will usually start from a dead stop at the bottom of each rep..with a 2 to 3 second pause. I use that same protocol on the bench and bench squats from time to time
A greatly overlooked exercise for the chest/pecs are pullovers. I prefer the bent arm version with either a BB or DB's. Also a great lat and triceps builder. Also affects the ab's strongly. One of my all time compound exercise is the pullover & press, a prime mass builder for the upper body. . When doing GVT (10X10's) of the pullover& press, I found my best gains.
Good Luck.