Irritation will typically occur on the sensitive skin of the frenulum located behind the glans on the underside of the shaft.
However, “on the shaft right behind the glans” might suggest that the irritation is occurring on the top side behind the coronal ridge of the glans?
For now I will assume that it is the skin of the frenulum that is being irritated. In which case, the underwear and pants will apply pressure on the glans which pinches the frenulum between the silicone ring. Movement then causes a rubbing action back and forth, typically when walking, which results in the skin becoming irritated.
To avoid this, start by tucking the skin past the silicone ring. However, this may not be sufficient, so you can hold the underside of the silicone ring with one hand while using the other to pull the skin at the base of the shaft near the ball-sack. This will effectively draw the skin back inside the sleeve. The silicone ring will then be seated directly behind the glans thereby eliminating any chance for pinching with subsequent rubbing action to cause irritation.
If you are in fact experiencing irritation on the top side of the shaft behind the glans… I would think that the same corrective measures would resolve the problem.
You can send me a message at the support email firstname.lastname@example.org where I can send the demo link via WeTransfer to your email. This video will give you a better visual on this proper set-up for the best performance and also the above described method for drawing the excess skin back down the sleeve.