[Adger Smith]

Rolling forward when you hit the brake has nothing to do with the low gear band adjustment. Low gear band adjustment has everything to do with the timing of the low band dropping out & the High clutches applying. Any one that has really looked at a racepack graph of driveshaft RPM / engine RPM can see if the shift holds low too long or lets it loose causing a flare in engine RPM. Comp racers & savy .90 class racers chase the bump on the graph to get it as smooth at the shift as possible.
The low band is already in full apply when you are rolling forward into the beams. It is line pressure or fluid vol required for a loose reverse clutch pack that makes the car roll forward. The rev clutch pack isn't applying quick enough to lock the tranny up. The cycling of the T brake before the final apply is filling the rev piston cavity with fluid. So when you make the final apply it doesn't take a full load of fluid to move the piston forward to apply the Rev clutches.