Well, I admit that I'm operating on theory but it goes like this...
Finding the right powder charge is largely based on the time the bullet spends in the barrel and where exactly the barrel vibrations are at the moment of bullet exit.
If you find an accurate load based on powder charge first and then start tweaking the seating depth, you are messing with one of the reasons the load was accurate... barrel time.
But, if you start with seating depth and find what the bullet likes most and THEN look for a load that gives you good barrel time, you're only messing with that one variable.
Light Trail Boss loads mostly eliminate the barrel vibrations as a variable because the vibrations start out much smaller and the bullet is going so slow that the vibrations have more time to die out before bullet exit.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.