I've recently been racing on an extremely low grip surface (not sure what it is - some sort of coated/textured asphalt "stuff").

I've managed to get the car (Tamiya RM01 with most hopups but original chassis) to perform passingly well on a combination of original Tamiya rears and HBR Fronts (other fronts also work with similar performance - Shepard/Enniti Hard, Jaco Purple). However, I want to calm the front down even more to give me a wider setup window. Due to the multi-use nature of the facility where I race, "wet" tire treatments are not permitted.

Try as I might I simply can't get my head around what tire might give me a generally lower front grip, if such a thing exists, given that I am starting from a fairly wide spread tire combo in the first place - any suggestions?