Flat bench uses your shoulders and tricepts alot more than dumbell presses due to the angle of each shoulder. So if you want you barbell to increase then work tris if you DB press is getting better then your chest is growing. Remember progress is progress.....
Thanks for the info.....My chest is definately growing, but my BB bench is just discouraging (to my ego).....I usually do tri's on chest day so they are pre-exhausted....do you think I should hit them a different day?
you can't really isolate the inner head since all three head work in unison to contract and extend your arm. Try lying skull crushers, I do these when i really need my bench to improve.... Also you can alter your routine so you do incline Bench first and then Flat. grnated your flat goes down dramatically but after about 3 months it is relatively the same weight as before and you are a lot stronger. Then switch it back and your flat bench will improve drastically.
definitely periodization, i have been increasing my barbell at a nice steady rate with no plateaus since i have put some organized periodizatoin in my routine, i usually go no longer than 6 weeks using the same routine for bench press.
The dumbell flat bench should actually help you with the bottom portion of the BB flat bench movement since the range of motion of the DB goes past what BB would go. It helped my bench about 15 pounds when repping in a very short amount of time.