Hello,
First, the gun to holster fit is off. The top of the gun should be completely closed. If it isn't, either that is the wrong gun or the spring has been stretched out of spec. Either or both may be the reason for the poor fit. This is NOT the correct fit.
Been since the late 70's but as I remember, the side snap was not functional? Could be wrong on that?
The Nelson, in my opinion was superior to the Hoyt. The Hoyt was an excellent holster in all respects. What I liked about the Nelson more was the additional strap around the trigger guard with a holstered gun. This gave much more stability and made a rearward gun grab so much harder.
I had two that I recall. The first was an issue higher ride with a straight drop. Great holster! Later I bought one that was a high ride also but with a muzzle forward cant. So much faster with a bunch less contorting of the wrist for a good solid grip and draw.
I did not notice the second snap on the thumb break as I always carried with the gun locked in. I would guess the second snap would allow the thumb break strap to be totally removed? Back then retaining straps were often taken off or not used at all. Also, on mine the outside snap was for show and a fake so a gun grabber might go for it first? As I said, it has been a few decades ago and many duty holsters ago.