According to the links, this mod is illegal for STX
"Q. I Autocross. What class will the kit put me in?
A. For Autocross, installing our ball joint relocation kit will put you in Street Modified. Unfortunately neither Stock, Street Prepared or Street Touring classes allow modifications to suspension geometry. Unlike an ALK, which relocates suspension points and puts you straight
into Prepared class, our kit adjusts a part of the "moving suspension," which is legal in Street Modified."
OP..Dialling in a good amount of negative camber to your front tires will make a big difference for you, and Megan coilovers allow you to do this.
Question, how does the car feel now on the limt? Does it understeer?