VacHanger Cap size doubts

Hey guys. Been trying to create a homemade vacuum cap to strech, but no matter how many threads I read I’m still not sure about a few details. I’m partially injured so I need maximum comfort.

When looking for it on Amazon/AliExpress, the size chart is (according to glans girth) S: less than 4,5 inches; M: 4,5-5,1 inches; L: more than 5,1 inches. These seem very short and tight, and low quality.

So, apart from commercial caps, is the glans supposed to fill the entire cavity? As for what I see in the posts and pictures, many do and many don’t fill it. Some of them even seem to have part of the glans out of the cap. It seems the size of the chamber doesn’t matter, does it?

I’m really struggling to find a proper cap because I don’t know what should I do. I’ve tried a few tight ones and I don’t think they will be comfortable because my girth is waaay bigger in the shaft, just one inch below the glans. Could this be a problem?

Btw, would you recommend me a pure gel finger tube or the ones they sell?

Thanks in advance.