Great philosophy, looking for a lens to fit your recently acquired lens case. 😀 I usually buy a lens and then start looking for the missing bits, but I do like your approach.
Which 3.5cm lens are you trying to fit in there? Did you try to store it with or without the lens hood? It does make a difference, at least all my Nikon SLR lenses need to be stored without the hood in their respective cases. Not sure about Nikon RF, hopefully someone else can help you out.
Jan