The take I got from some old racers was that pro-ox was that there was no fuel test for it because of its high evap rate and would be gone by the time the fuel was tested. Word has it you could hold some in a glass and with the heat from your hand ,you could see it evaporate.
Another trick a back in the day racer told me about, (Before there were burnouts), He would drain the secondary bowls and fill with a "Hot Mix" then would idle up to the line, get the signal and mash the throttle and dump the secondarys getting that extra hit. By the time the race was over, bowls would be filled back up with gas. He said he made more money by teardown protests than he did racing looking for the hidden tank