Rebound effect after pumping

I'm noticing a rebound effect in my penis after pumping my member is retracting a bit to create a smaller length girth is great. Maybe add some manual stretching back in?

All in currently doing is burst pumping 2.5 inhg to 5 inhg then pulling on the tube to get 10 to 15 for an instant. depending if it's a working or recovery day. Any advice is appreciated in advance.