I’ve started adding folded paper towels to the bottom and around the sides of the cup before putting it into the holder. 2 reasons: It fits better, and also keeps it from the dampness coming through and leaving the marks on tables, etc that I got these to prevent in the first place.
https://www.amazon.com/Stainless-Insulated-Sonku-Neoprene-Protective/dp/B07RJWLYDC