Muscles have particular range of motion, and doing an exercise a certain way may only utilize part of that range of motion, and affect the stabilizers, but, it does NOT change the muscle shape, nor overall range of motion, nor is it particularly more effective. You'll want to avoid movement that bind on your joints, too. I.e., your biceps have a certain set of muscle and each muscle contracts in a certain path. There's no changing that.
Generally speaking, flat bench presses will involve more anterior deltoids than a 45 degree incline press.
Dumbbells ALWAYS provide more range of motion and involve more stabilizers (you have forces in multiple directions).
You should consult a muscular anatomy chart, look at the muscle, and walk yourself the range of the movement, and FEEL, the muscles affected.
For chest development, full range, moderate to high reps (8 to 12 and beyond), dumbbell incline presses are superior.
I've seen many folks in the gym doing partial reps. That's stupid, and a formula for future injury. You should do your movement through a full range of motion.
A stretched muscle is not only bigger, but, also, less prone to injury.
Unless you're power lifting, 1RM, 3RM, lifts are not something you need to be doing.
I literally touch my chest with dumbbells when I do dumbbell presses.
Keep the reps up, and EAT.
You should be careful not to overdevelop your anterior deltoids in relation to your posterior deltoids (I.e., don't do military presses to the front along with lot of bench presses without doing a bunch of posterior deltoids work.) If you do, you'll run into shoulder impingement problems that you almost certainly could have avoided through proper balance.