I've never raced on a tar type of track other then old tar covered parking lots.
You could experiment with the pinion gear and radio settings. The radio might not be giving you 100% full trigger. I had that problem before, changed radios and my M-05Pro suddenly got faster. Gained 1.5 seconds a lap and put me near the top of the speed charts with everyone else.
My guess is this being true for you too.
If you can, try and borrow another radio/receiver for a few hours to see if that made any difference. Wish I still had my Mini, miss that class soooo much.
BTW, TCS rules will allow 21.5 brushless in the mini class this year. Speeds shouldn't be all that much faster over the silver cans.
Associated TC3 VTA & TC6 USGT