“F guff, how did that rambling diatribe have anything to do with the OP's question? Auto mechanics? I thought this was a reloading forum?!”
Snuffy, some of by best friends are/were auto mechanics, but when it comes to rendering a rifle/pistol scrap I do not believe the detonation rational and that part where they tell me “What you do not understand is there is are two flame fronts and they meet in the middle etc., etc..”
the case forms a column for the powder between the case head and bullet base, I am the fan of igniting my powder column from the head of the case to the base of the bullet, I do not want anything between the case head and bullet base but powder, but if I do put something else (besides air) between the top of the powder column and bullet base the something else is going to compress, if the material that is placed between the top of the powder column and bullet base is abrasive a ring can appear. I know, some pack toilet paper in the case to keep the powder stacked against the primer, I am out of John Wayne toilet paper, even with John Wayne toilet Paper, when compressed with thousands of pounds of psi, toilet paper is abrasive.
I am not the fan of reduced loads, I believe powders are position sensitive, some more than other.