Happiness percentage of non-breeding cats

[Lumiae Resident]

First of all, thanks for reading this, I just have this burning question which boggles my mind about cats happiness;

I have 2 perma cats and 2 non-breeding cats (passed 121 days) running around on a 10 meter range, and I've noticed something about their happiness levels. My 2 non-breeders are constantly around 93-94% in happiness while my other 2 perma-pets' happiness hovers around 86-89% but never over 90% unless I cuddle them. I don't cuddle my non-breeders, I don't interact with them nor is there milk out.

I'm wondering if its just my non-breeders being quirky and insanely happy or are all over 121 days old cats always happier than perma-pets?