I have a TON of experience with exactly what you are referring to. Inzer 4" lever belt (13mm), testing belt positioning, and George Leeman experience.
I know exactly what you are talking about with this belt. I've tried multiple things over the past year. For me, the belt restricts me from getting low enough to start the pull, when I wear it in a normal position. When I wear it in the leeman position, high, I can pull the bar up to my knees without even trying, but I have back injuries in the past, so I cant' finish past the knees (physical pain without a belt). You definitely feel way restricted when the belt is high, but I also know it needs to be much looser when it is high.
When it is low, basically on the hip bone, it slides up when you drop down into position.
When it is mid belly, it restricts you from bending down to grab the bar.
My solution was a new belt. But, here is how I came to that conclusion. I purchased a very cheap Amazon leather belt, one that is 2" in front, 4 in back. This allowed the tightness I need on my lower back, with the small front which didn't restrict positioning at all. But, it's cheap, and stretches. Next I started using my Ratchet belt I've had for a while. This thing is great. it's thinner, more flexible, yet you can crank it down to really give support.
So, for me, my conclusion wasn't the lever is the problem, nor the 4" of the belt, but the 13mm of the belt and the inability for it to bend at all was my problem. My ratchet belt is like 10mm, and you can fold it in half, yet it is strong as hell and doesn't not stretch. For me, I wear it about as low as I can go, just above my butt (again, for back injury purposes), and I crank it down as tight as I can possibly get it. If I don't, then my back twinges about mid pull and I get injured, pretty much every time.
For you, I suggest doing something similar.
Fast forward to 1:15, that will show you everything I tried on my deads with the belts. I suggest doin the same, video taping each lift, and comparing what is best for you. My form is shit in these videos as I was on the Leeman training at the time, and he pushes his form onto you, which just doesn' work for me, so ignore the form, but pay attention to the ways I try the belts.