Hi, I think the main reason why most people don't get big changes is that no CONSISTENT medium force is exerted through the tongue. That's why Chin Tucks work so well, because they exert this very force all the time. However, you can't chin tuck permanently, because it would harm the neck. I observe myself again and again how I don't use force in situations where I don't concentrate, even though I am already mewing over a year. How do you do that? Or are you satisfied with Suction Hold? Unfortunately I also have neck and back pain, which makes it more difficult to hold the as a whole
I think creating vacuum trough swallowing and then using medium force with the tongud could help
I also find that when I am focused on something else my tongue posture is weaker.
I believe it is natural to use a suction hold and soft mew with good body posture. If this is done at a young age then the maxilla will grow how it was meant to grow: forward, downward and outward (wide palate). However most of us are now adults lacking the forward and outward growth. Without the advantage of childhood growth on our side, we must rely on bone remodelling and I believe hard mewing helps a lot to speed this process. For body posture when the maxilla hasn't grown forward the jaws and tongue are too far back in the airway and this subconsciously makes the body want to adopt forward head posture to breathe better. A way around this is to put reminders up to hard mew like @Azrael said he does and to have good body posture at all times. Lifestyle changes like a standing desk and sleeping on your back can help aswell. But beware that back sleeping can cause sleep apnea if the maxilla is too far back. Hard mewing is definitely more difficult than soft mewing but after some time the tongue will get stronger and it will get a lot easier.