Let me try again. "Cheek weld" to me is an issue for target rifle or other shooting events where the head (cheek) has to be rested on the stock.
When you mentioned a ladder test, I was thinking in terms of shooting a scoped rifle off a bench or in F-Class. A precision rifle loaded with precision ammo will show the effect of every variable in the system. In a ladder test you are trying to see the effect of one variable - powder charge. All the other variables should be reduced as close to possible to zero.
Your head can be a HUGE variable and the OP was astute in identifying it as an issue.
In a typical shooting rig, the rifle is supported under the forend and at the heel. By resting your head on the rifle, you are applying a variable weight of several pounds on the unsupported part of the rifle. This induces some flex on the stock/bedding and also creates a variable to the way the rifle moves on recoil.
To make the rifle react as much as possible the same way on every shot, the head should not touch the stock. As mentioned, I control this with whisker pressure to position my head in the exact same position, without any pressure on the stock.
Most rifle are heavy enough that they can be shot "free recoil". That is, the butt is positioned a half inch or more off the shoulder, so that the rifle recoils without any influence of either cheek pressure or shoulder pressure.
By removing these large variables, subtle variables like 0.3 gr more or less powder can be seen.