If you are shooting during a bit of mirage (and wind changes) it will be hard, if not impossible, to discern condition and shooter influence on vertical. However, if you are using a solid front rest with a proper fitting front bag and good rear bag and very consistent shot release you can assume your influence on vertical is minimal. That being said, in 'perfect' dead still/no mirage conditions I can easily induce vertical with a variation of shoulder pressure and even when I feel my technique is at it's best I realize a slight change in my position behind the rifle turns a .3 moa load into a .5moa 10 shot load. Calm overcast or light drizzle conditions can also be outstanding test conditions as you will have almost no/ zero mirage and the drizzle is the best wind indicator you can get IME.
edit- also, if you find a load that shoots flatter some days and more vertical on others in similar conditions try adjusting the fore-end stop on the rest and see if you can tune that out. I have one very flexible as well as a shorter more rigid F-open stock that both are sensitive to the position of the stock in the front bag (as in overhang). The flexible stock is more sensitive in my hands.
Robin