E-crt

I'm starting a CRT conversion and I'm curious what pinion are you guys using with the Kyosho 46t plastic spur gear? my motor is going to be a Neu 1515 1y on 4s and a Quark 125B esc.

I was trying the worst case senairo first and I noticed that if I put I put a 9T pinion on the motor and hold it in place the motor hits the diff cup before you can get proper mesh.