Sizing Up for an MM Jail Bird Device

I’m quite new to this and attempted a search on the Forum, but “JailBird” kept coming up too often so nothing useful showed. Here goes…

The sizing rings just arrived (apparently Mature Metal is based in Weatherford, Texas—I’m only roughly 20 miles from there!). I suspect I fall into the “high and tight” category because even getting that 2 1/8 ring on was a struggle. Once it’s on, it feels quite snug; while I can push one finger up to the knuckle as directed, it still feels a bit uncomfortable. Should I size up by 1/8 or perhaps 1/4 inch?

Additionally, the ring that sits comfortably around my flaccid shaft is slightly too tight at the head. Which should I prioritize: the fit for the shaft or the head??

Regarding the gap, would it help to measure the thickness of the scrotum at its base? What’s a reliable method for estimating this?

As for length, during the day mine measures about 3’. Does that mean I should choose the 2 3/4 option?

Thanks in advance for all your advice!