I agree with going to 5hg. Or go for more time. Maybe even record your workouts. You can always progress with your PE sessions whether its intensity, volume, or density (volume/time). Example: If you pump for 4hg for 30 minutes, go for 5hg for 20 minutes next week. Your volume didn’t increase but your intensity did because you went up to 5hg. Work your way up (slowly!) to 5hg for 30, 45 and eventually 60 minutes maybe. Come to think of it, your volume would be how long you are going since you aren’t really doing reps. Reps x weight (Hg) would equal volume but since you aren’t inflating/deflating constantly (which could be a rep), the “rep” number would always be “1” if you pump and don’t deflate until you take a break.
I’m not a big numbers person but seeing perpetual progress in one way or another would be good! Overload is needed for growth, IMO, but overload doesn’t mean beating the crap out of your dick. It means increasing the volume, intensity or density everytime one way or another in a systematic way.
Hope that helps a little and hope I didn’t confuse you :)