Problems with fit - slipping or restricting blood flow

I'm pretty new to any longer-terrm chastity, though we've experiemented a bit before this. I had an inexpensive chinese device from Amazon, and got in trouble right away when I tried to wear it for 24 hours. I was using the largest ring- 2" diameter- but it seemed too tight. It was uncomfortable, and seemed to clearly be restricting blood flow. Not too far in, and my scrotum had bulging capillaries, and was trending purplish. I tried to tough it out while working it through, but it didn't work very well, so I removed that one. I have ended up with a Bon4M, and requested larger rings from them to try to fit better. The Bon4m rings are more comfortable ( they are wider ), but I'm still struggling some of the time. Here's what I have on this at the moment:
1) The 50mm ring just doesn't work- it's very uncomfortable right away.
2) The 52mm ring is fairly comfortable, but I end up with on ongoing dull ache in my testicles. I'd describe the pain as a mild form of what we called "blue balls" in high school- that feeling when you were making out forever, all turned on, then had to stop. I have managed to wear this over longer time periods, but I'm worried that dull ache means it's causing damage. With this ring, I can barely force a finger under the edge of the ring, so I think it's a little too tight.
3) I tried the 54mm ring, which doesn't seem to have the "dull ache" problem ( at least not as much- just a little from time to time ), but this ring will end up allowing my smaller testicle to escape, leading to pain and trouble in its own way.

As I was trying to find an answer searching around on CM forums, someone suggested that someone with this problem might need a bigger ring and a smaller gap between the ring and cage. I hadn't considered that- after the scary problem with the chinese device, I started with the largest gap and assumed that needed to avoid cutting off circulation.
I tried the next size smaller for the gap with the 54mm ring, and that seems the best so far- but it still has my other problem. With the 2 wearable rings ( 52 and 54 mm ), the device seems to tug down and slip a bit off. I can fix it with a 2-handed crotch grab- holding the entire device up and tight, and carefully tugging the scrotum skin back "into" the ring.
The problem is, that doesn't last long when I'm standing. I'm looking at belts, but I'm not sure that will solve the problem.
Anyone have other ideas? I'd like to just wear this thing, not keep adjusting it. Help!

 

Thanks, @Littlejt1 , I think the ring/gap adjustment is part of the problem, but not all of it. It's possible that I may need a ring size between the two that I have available.
The bon4m devices have fairly good adjustments available- I got a set of 7 rings, with the smallest being slightly too small for me, and the rest increasing by 2mm diameter each. The attachment between the ring and cage can be set to 3 gaps ( 8/11/14 mm ). The cage and ring all together are a bit heavy, which I think might affect this. It ends up kind of like hanging a weight on all of the equipment, so it hangs down straight between my legs when I'm standing. I imagine it slightly pulling as I move, and eventually pulling to a place where it's a bit uncomfortable- and I think would get more so. I hold the device and slide the scrotal skin out from under the ring to on top of the ring. Walk around a while, and repeat. Anything tighter on the ring or the gap adjustment and it seems as though it starts restricting blood flow.
With the current setup, the testicle pain now seems to be gone. I'm not sure if that's my body adapting, or if it's just fitting better now. It still slips a bit. Maybe I need to switch to a plastic cage that would be lighter weight, I'm not sure. I'll probably pick one of those that is widely liked- maybe the Cherry Keeper that several people have mentioned for their adjustments and ring size availability. Guess I'll be trying the support belt when that gets here.