Rage did a comparison for non-season vs. S28 adjusted (5k, 15 min) clears, and the average was a little over +7 tiers. With some builds as high as +10 tiers: State of Set Balance Report - #77 by Rage-13139
Math on the damage numbers suggests something around +7-10 tiers is a reasonable estimate as well.
I’ll do an update for all sets in a few weeks, that may have changed a bit as people start doing higher effort clears in season.
+20 tiers is a bit generous though I think.