CGBP and Floor Press place more stress on the triceps than other pressing motions. (At least this is my understanding)I see it as how you keep the push towards the lift, it depends mainly on CNS adaptation and carryovers from other lifts (IE Floor Press) and also with the direct assistance work.
For me doing floor press and/or heavy CGBP is what helps the top portion of the lift, IMO it is a mix of getting used to "keep pushing" through the lift (so more motor coordination and CNS involvement) and also strength from the assisting muscles that are directly engaged in the lift.
Which I thought was the point of adding them into a program to strengthen the triceps for the lockout of the bench press.