I just finished having my system put together, and I am wanting to practice dry firing with my rifle mounted on a tripod, while sitting on a three legged blind chair. I am seeing 2 different heights. One is a perfect butt/shoulder location, or a perfect scope/eye location. All of this is with flat ground, with a flat target location. I am guessing the differences is between about 4-6 inches. No recoil with this caliber or system. Thx!