Shipping Rates Off When Using A Negative Percentage

Hello all,
When I set a negative percentage number in the shipping methods>UPS Next Day Air>Shipping charges> Cost dependencies> Set by Minus -36 percent, the shipping charge returns as a negative number. Shouldn't it just subtract a percentage from the live rates? This happens when shipping to the address I've tested below, shipping from 93722 in the US
1563 Celeste
Clovis, CA 93612
I'll include screenshots for reference.

Any ideas on how to resolve is greatly appreciated.