I had exactly that problem, but nor more.
Bought a set of "Stomper" grip pads for the tank, and now use my knees to help me keep well back in the seat. 1st track day looking at the pictures had a 4-5" gap between the back of the seat and my butt.
Prior to this I was always jamming into the tank, using the grip pads, and proper knee position, I seldom slide forward any more.
It also helps your body postiong and hanging off. Before I had to swivel my hips to hang off, now it is a strainght lateral shift of my butt and upper body.
Try them, you never go back.