I found out the hard way to not leave my hand on the shifter handle with me arm relax on one of my old bracket car that ran high tens, my hand flew off the shifter handle on the first launch on that car and hit the roll cage hard
Next was the G force moving my arm back making me short shift it out of 1st gear when I stiffen up my arm before launching that car
I finally learned to stiffen up my arm and hand so the G force wouldn't make me screw up the shifts
On the early Winters and Fairbank shifters I learn to push the shifter lever over towards the passenger side of the car on the 1-2 shift so it wouldn't slide directly into 3rd. gear