I've mewed naturally my entire life, yet I have a slightly recessed chin and not the most ideal maxilla placement. But I have also slept with my mouth open while night mouth breathing my entire life, so I suspect mewing at night is equally if not more important. I've fixed this now with mouth taping, but I thought I'd throw that out there.
Taping your mouth shut does not mean you are mewing at night. It just forces you to breathe through the nose. Getting the back of the tongue up subconsciously at night and actually mewing is different.
But when my mouth is closed, my tongue naturally mews. The tape closes my mouth, forces me to breath through my nose and along with that the tongue position just happens right.
6-10 hours every day adds up pretty quickly so I totally agree with night mewing being something to really keep an eye on
In that case tape it shut. When I used to do it, it messed up my conscious mewing before falling asleep, because the lips were in an awkward position and I ended up mewing regardless during sleep, so I stopped taping a week ago. I did tape it for the first month tho.