First of all, a bit of background. I have been interested in bondage and orgasm controls in years. Didn't matter to me on which side I was as long as someone was in control (I am pretty sure there are some deep dark psychological issue for that but, I couldn't care less

Luckily for me, I found a girlfriend that is almost as kinky as I am. It still took me 3 years to bring up male chastity and when I did, she seemed to like it. Few weeks later I showed her a rel CB6000 while one of our trip to the adult store to get order stuff. She did like the idea but didn't want a CB6000.
Her condition for the devices were that it has to be easy to clean, it should not smell bad and safe (not as I can't get out of it but as it shouldn't hurt me). So I ruled out the birdlocks, bon4 and the cb6000,3000,2000 and the curve.
I was left with those steel devices that you can get on the net for around 100$. Users of those devices did tell me that some of them had a tendency to rust due to lower quality steel being used. I started to look at more expensive and custom fit devices and ended with Maturemetal. 316 surgical stainless steel is pretty much the best I could ask for.
My issue thought comes with the sizing. I did order the sizing kit and followed most of the measuring guide on an other popular chastity forums. After 2 weeks of measuring, I thought i was good to go. Then after poking around I saw that what I ended up with was a lot bigger than the measurement that some other people posted and it got me extremely worried. Which is why I am here, writing a dreadfully long post and hoping that some people who have worn or are wearing the device could enlighten me.
I am very scared of having the sizing wrong since this is my first device and I have no experience. I would normally buy a cheaper one for starter but that is currently out of the question. I know that everyone is different but I measurements seem so out of place that I think I might be just not doing it fine.
So here are the measurements that I have.
Base ring : Oval, 2''
Length : 3 3/4"
Diameter 1 5/8"
Gap 3/8"
For the base ring, I got to that measurement by wearing the biggest ring, getting hard, checking if it hurts, pinches, or if my balls and cock changed color. I did that until it happened and then when 1 size up and ended with the 2" ring. I slept in it for almost 2 weeks and it never woke me up. It did pinch after a while but I started to shave and it stopped so I think I am good for that ring.
Sadly, for the rest I couldn't do what is in the guide so I based my measurements on the guide that game with the sizing kit. When flaccid, I measured from the tip of my penis to the base where it meets my scrotum and subtracted 1/4". I ended up with 3 3/4" which seems way to long. I know there is shower and grower but due to the fact that I haven't found clear explanation and that I don't speak English very well, I am not sure that I got this right.
Same thing for the diameter. I used the ring when flaccid and measured. I ended with the 1 5/8". The sizing guide said that the ring should be snug but not to tight. Could someone explain this to me. I am unsure of the meaning and possible examples would be great.
I will greatly appreciate any help anyone can provide.
PS : I am guessing you got this from reading my message but English is not my 1st language and therefor I apologize for all the mistakes and it some of the stuff I wrote made sense for me in French but not in English.
Thank you very much