The rest set up you have just is not the best, I would get a rear bag, it will make a big difference. Protektor makes some nice bags, and if you have it shipped to a FFL they eat the shipping. http://www.protektormodel.com/

Anytime you shoot off of a bi-pod you need something under it to absorb the shock, like cardboard, carpet, or something like that. What happens is the force goes right don't the legs and into the concrete and cause the jump. MR F. uses a hard piece of foam rubber and it works great for him. Putting something under the bi-pod dampens the force coming down the legs, but it also allows the gun to recoil back, giving the feet of the rest something to slide on.