I can only go by my little cats symptoms of having cystitis and that was straining to wee.
Having lost Harmy to Familial Nephropathy...he certainly never had cystitis

quite the opposite in fact, he wee'd for England

I dont think I've read anywhere that cystitis is one of the symptoms

And I can really only advise you going on how Harmy was.
If you are worried, then ask your vet if he/she thinks a proteinurea test on Honeys wee to rule out FN would be a good idea. But I dont think you need to worry

I have suffered from recurring cystitis since I was a child, but I now manage it by making sure I drink plenty of water. To help my little cat I mixed warm water into her cat meat to make sure she had some fluids
edited to add that from your posts regarding Honeys weight,it would suggest that you have no problem with FN. I could never get proper weight on Harmy. It was always put down to him being so active (and believe me he really was!), but from research, it is one of the symptoms. So the fact that Honey is supposedly overweight doesn't indicate FN.
It may be contributing to the cystitis tho
