I think the middle is the anterior delt help. I have a huge flaw between 2 and 3 boards. Usually strong off the chest and at the top, but right between those 2, and I sputter out.
BTB is right. CG will increase the ROM of the entire lift, therefore training more supplemental muscles. However, it is hell on the shoulders when done too heavy, too often
I recommend heavy board work, CG bench, cambered bench, and incline bench to help with the anterior delts, to help get them to firing throughout the middle of the lift rather than just at the top