Sit at the lights and flap your arm up and down with your hand flat out of the window, then get to 50-60mph and do it.
Ive never restricted my gear and funny enough all my models have super reliable retract operation. On the Mephisto the forward retracting ER50 units have a speed limit...or they just stop moving.
The extra valve gets rid of extra joints and tubing length if you plumb it right, and you are not dividing the supplied air by three, it works on set ups that are ‘just on the edge’