Ab Forward Roll Tips?

I’m just starting CT’s Ab Training for Athletes 2K3 program. The forward roll (I use a barbell) is the one exercise that I just can’t seem to get right. His advice is to really flex your abs through the whole range of motion and don’t go down further than you can handle. I think I’m doing those things, but I still don’t feel my abs working like they should be.

Anyone have tips on how to perform this exercise properly and really hit the abs the way it should?