plugins\fBaseXtensions\XML\AcceptTieredRiftRewardTag.cs
change
Line 108: var rankedGems = SelectableGems.Where(g => g.LegendaryGemRank > 0 && GRiftLevel-g.LegendaryGemRank>-2).ToList();
-3 = 8%
-2 = 15%
-1 = 30%
0 = 60%
etc.
I set it to -1 to upgrade the lower ones first...