Possible issue with recombinator success chance calculation

I'm not entirely sure, but this looks like a bug.

When selecting flat Lightning Damage T1 in the first ring and Strength/Dexterity T1 in the second ring, the success chance is 14.77%. However, if instead of Strength/Dexterity (T1) I select Intelligence T2, the success chance drops significantly to 3.02%, even though the chance should increase due to the lower modifier tier.