Supreme-
There are two types of numbness hangers may experience: Acute and Chronic.
Acute numbness is a temporary condition akin to having your arm or leg “fall asleep” due to a lack of circulation or because of pressure on nerves.
Chronic numbness is an indicator of nerve damage - likely caused by long term oxygen/nutrient deprivation and/or direct physical damage to the nerves themselves.
Though it is highly unlikely that either of these conditions will remain permanent they are to be avoided.
In the case of acute numbness you have to take a very responsible attitude and consider whether what you are feeling is simply an end of set ‘nap’ or a possible warning that damage is being done.
A good indicator as to the nature of what is happening is the frequency of these episodes and the length of time they persist. If full sensation always returns within minutes it is likely you are safe. If the numbness persists or is erratic - meaning, it might last two minutes here, 20 minutes there - you are being given a warning that something is not right. Proceed with extreme caution, if at all.
Everything I just said assumes that the numbness you are experiencing is not total. Meaning, you sense a slight loss of sensitivity instead of a complete loss of sensation. If you end a set and cannot feel anything from the lightest touch to intense pressure - or heat and cold do not register - you are on thin ice. Even if sensation quickly returns.
As for placement of your hanger and its role in this matter, you have to first understand that the damage you risk will not come from the hanger contacting with the glans. The most likely cause of chronic numbness will be through excessive pressure on the dorsal nerve bundle that exists on the top of your shaft directly behind the glans.
There can be other causes, but this is the most likely.
Wrap too can cause numbness. Be sure not to wrap too tightly. When you do this you are creating a noose that strangles the glans and puts undue pressure on the dorsal nerves. Keep things loose enough so that you can at least urinate while wrapped.
Jelqing between sets and after your routine is a very good way to restore full circulation, so be sure to do this. Your suspicions about set time and weight and how these things affect the health of your unit are important things to consider as well. Never hang so much or so long that you experience pain - you should be comfortable, not watching the clock and praying for the end of your set. If you find yourself in this frame of mind, cut the set short and/or lower your weight.
-Cap