I have some opposing points of view for your consideration:
- Bones are malleable, but they're not that malleable. Maxilla is still one bone, and by pulling it to any direction pulls the whole maxilla in that direction.
- I'm finding it hard to see your logical sense in how upward force would repress your orbitals. If anything, moving the maxilla and zygos higher and forward should give the whole eye are more support, unless you've been pulling towards the back of your head (which would be quite difficult in the first place).
- Mewing with posterior tongue gives constant force to similar direction than facepulling, and it nearly never makes facial characteristics worse
Unless you took good before and afters, I'm pretty convinced that you're just experiencing placebo, because from personal experience I know how easily it can happen. The way I perceive myself in the mirror fluctuates from day to day, and other factors like amount of sleep, water retention, exercise and diet significantly influence daily appearance.
Personally, I've been beltpulling mainly forward, since as a kid I had a nocturnal appliance that pulled my upper jaw backwards towards the neck. I've seen some improvement in overbite, but most dramatic differences have started coming from correct head/body posture and strong mewing throughout the day.
It also helps to keep your lower jaw as relaxed as possible when belt pulling. You are able to anchor the belt to the upper back molars and the area behind it, "bite" down with the upper jaw by tilting head downwards. Then you should be able to just relax your face and pull forward.