While I’m not the expert, based on what you’re describing it’s a girth issue more than a length issue. The stealth I wear fits fine without retraction issues and my head never turns purple.
That only happened to me when I had my original one that I tried to make work. It was so much hassle and I’m so glad I got the right size. It’s night and day how much more comfortable you can be when it fits and you can move normally.
I actually wore a smaller size extension sheath without the ballband last night to work out at the gym. Was doing push ups, sit ups, and all kinds of other cardio bend over jump up walk down pushups… no retraction and was comfortable. If it was uncomfortable at all it was because I’ve been too lazy to buy extension sheaths in the larger size I usually wear and the silicone ring is a bit tight on this one which causes my head to be fully inflated and the friction of that against my underwear with all the movement was lol. But I can have that even without the stealth, just not as intense. Still, my head was never purple!!
Head turning purple or painful is dangerous, never let that condition last long. It’s your Dick screaming for oxygenated blood and you want that to keep sensation for life!!!