The wisdom offered in the posts above is good. It's more complicated than you think.
Using velocity (not pressure) I varied OAL and powder charge in pistol cartridges to see how much the OAL affected performance, and how you can adjust the powder charge accordingly to maintain the same performance. I was seeking a convenient formula for each pistol cartridge I load.
Here's the conclusion:
It isn't linear. So there is no rule that applies safely in each case.
Not only is the curve non-linear for seating depth, but it's a different set of curves for each cartridge, powder, bullet weight, bullet type, and barrel length. Also, each combination changed the point of impact on the target. Sheesh. After several thousand rounds of shooting fun, I gave up the exercise.
And don't forget the caveat that I was measuring velocity. Who knows how it affected MAP chamber pressure.