What make of front rest and rear bag you running? If you find you are way off from shot to shot, it could be the equipment or technique.
If the bottom of your rear bag is round that is an issue. A donut will help that as long as not to concave. Protektor are some of the best bags out there. I prefer tall ears, with slick fabric. My bag has a soft bottom and I use a donut. There are also bags with a thicker hard bottom. This will work as long as the bottom has a bit of a convex shape to it.
If the bottom of your rear bag is round that is an issue. A donut will help that as long as not to concave. Protektor are some of the best bags out there. I prefer tall ears, with slick fabric. My bag has a soft bottom and I use a donut. There are also bags with a thicker hard bottom. This will work as long as the bottom has a bit of a convex shape to it.