-spell cost % increase spell cost when having negative spell cost?

https://hppeng-wynn.github.io/build...00O10009I1001iO1001iO01B1B05050D0J0rtsrMRTbv0
WynnBuilder build:
> Gale's Sight
> Diamond Dust
> CR-1969F9F5+5+5+9i91
> CR-1969F9F5+5+5+9a91
> CR-18O8O8O8O8O8O9m91
> Summa
> Breakthrough
> Renda Langit
> King of Hearts []
> (Has Tomes)

This is my lootrun build, and teleport cost is 1,1,1,1,1,3. (-17,-17,-12,-7,-2,3)
But when I replace Diamond Dust with The Jingling Jester, teleport cost become 1,1,1,1,4,9. (-11,-11,-6,-1,4,9)
So the -30% teleport cost made negative teleport cost higher?

I think -spell cost % should function like health regen %, doing differently when health regen raw is positive or negative (an example is Nether's Scar).

 

There's some funky math stuff that happens when you mix a large enough amount of -spell cost raw and -spell cost% together. For a clearer example, pre-2.0, you could have a -120tp cost Warp, but if you were wearing a Mirror's Edge with high -second spell cost%, it would end up only being about 30 free teleports