Similar issues have happened to me. I got into Stealth a little over a year ago. When I measured I would get excited and it would measure wrong. I also made the mistake of measuring first thing in the morning, when my testosterone was at its peak. So over time I actually ended up going down 2 sizes in girth before getting the right fit. For me the best time to measure is in the afternoon or evening after work, but it sounds like you have those bases covered.
Now that I am at my correct sizing for all day wear, I still run into the tightness issue when I get a new one. For me it takes a few wears to break it in and stretch out a little. But then it will last for months all comfy and extended. When I was at a bigger size, at first it would go on easy and last all day, but only for a couple of weeks. Because then once everything stretched out I would have issues slipping back inside before the end of the work day, which was not comfortable. So yep, it is pretty tight for me in the beginning, which is funny cause that just gets me more excited adding additional tightness. Just make sure you don’t get blue as you don’t want to cut off circulation, that would be too tight and in my opinion need to be removed and reset.
I also have both the strap and non strap versions and I love them both, for different reasons. I also have testicle retraction that sometimes cannot be gripped by the strap and one of my balls will retract up which gets uncomfortable. So that is one reason I have the strapless. But I also have 2 MagVolts which greatly improved the retraction issue for me. A lot of times when wearing the strapped version, I have on 1 MagVolt. I can’t think of having the retraction issue with the MagVolt on, but it’s possible it has happened I just don’t remember. When I wear the strapless version, most of the time I wear 2 MagVolts with it, which I would say is my favorite option, but it’s a close race because I really do love wearing both!
I suggest giving all of the options a try to figure out what works best for you, strapless and the MagVolt. So that’s just my 2 cents. Hope it works out for you! Stealth customer service is so awesome, so they will be able to help you resize so that you can be all comfy and extended like the rest of us!