My point is that assuming you are shooting at 100yds you have a half MOA difference between best and worst with the same ammunition. That isn’t consistent enough to find what might be fifty or a hundred thou improvements.Best 0.5" and worst 1.209" STDEV of 0.202 those were the factory HPS. But your point is exactly why I was asking the experienced reloaders for some numbers to compare with. How close should the groups be and over how many groups do you average to make an assessment, before seating depth effect can be observed and identified?
For instance I loaded 87 Vmax in my 243. The worst group was maybe 1.2” the best just over .5” loads 2 & 3 and 7 & 8 were all about that. I split the difference of 2 & 3. Then tweaked the length slightly ending with .400”.
So as the first improvement by powder weight gained the difference between your two extremes. You wouldn’t see the improvement, let alone the tweaked depth one.
I don’t mean to be insulting but practice practice practice. Keep everything as consistent as possible. If you have one take a 22lr and use that while your rifle cools.