From everything I am reading you need to adjust the bottom nuts or your wrap thickness. Most likely it is the bottom nuts. If it is completely closing and yet not gripping strong enough then the nuts need to go down more. I believe this would be a turn to the left.
There have been people with a lot more and less girth than you, that have been able to get it to grip. In my opinion this is absolutely the hardest part of the hanger. Getting the nut settings with your girth and wrap. However, once you get it correctly it will be a world of difference. It should grip so tight that the hanger will not slide forward at all.
Once you have those bottom nut settings correct you will probably not touch them for a long time. Even when you do it will just be a slight quarter turn.
Now when I have those settings correct then I have a routine that I follow. I tighten the hanger squeezing all blood back from the glans. I use my other hand to bring both sides together so all the stress is not on the wingnut. Then I let is sit for a moment. Then I try to give the wingnut another turn or two while gripping both sides together.
If it is unable to turn then I start adding weight. I go in 2.5 pound increments but slowly. I am feeling for any motion forward of the hanger, and I am letting my penis adapt to each weight change. It is very common for me to tighten the wingnut a few more times during the process of getting up to my full hanging weight. For my first set of the day it could take me 3 to 5 minutes to get to full weight. The entire time I am continuing to see if I can tighten the wingnut some more.
After the first set of hanging, this process will only take maybe 1-2 minutes for each following set. No matter how hard I tighten the hanger, there will always be a little gap in the top teeth. They will never be completely meshed. If they are meshed this is a sign that your bottom nut configuration is wrong.
When I have the hanger completely tightened it has a vice grip on my penis. It will not be going anywhere. When everything is perfect it will feel like I could hang any amount of weight. Regretfully it is not always perfect. My girth is not uniform down my shaft. So I try to find a reference point for the front of my wrap. I then try to keep the exact same distance from the hanger to the front of the wrap. The more consistent you are with this, the much better your hanging career will be.
My first 6 weeks of hanging where just getting this process correct. I believe because I was so careful in learning this stage, I have been able to avoid injury. Under 10 pounds of hanging you can make more mistakes. But as you increase weight the mistakes compound. There have been people that hang with a blood plug and they start losing sensation in their penis. This is not a good sign.