Sorry for the late reply Jhark,
My first thought is that you had the Innerwear inside out as this is what leads to the silicone ring folding under and the glans slipping back inside the sheath. However, as you mention that you are using the ES then this would be highly unlikely. I would recommend experimenting with the load distribution by tightening coils along the entire shaft for a more secure fit. What size Corkscrew are you wearing? The size and weight will have a big influence on the dynamics of wearing the device so this is always a consideration as well as experimenting with removing some coils to optimize the experience.
With respect to the fit you have now and going to a smaller silicone ring… this would be a more subtle nuance that I am not in a position to say. I think that you are in the best position to make this sort of decision and then see what the difference is as a direct comparison is the only real way to get a definitive answer to the question of size adjustments for the best performance at this level.
Photographs could help provide more information but I would have to see if there is something more obvious to comment on. Often times there is.