How would you know when the tongue in the right position? You would not, because there is no right position for the tongue in a skull recovering from craniofacial dystrophy. Mewing is not necessarily a static activity. What feels like full tongue posture today turns out to be just 80% of what you can do the next month. As your skull and body keeps changing, you have to continuosly re-learn tongue posture.

As for practical tips, try to simultaneously pull & suck the tongue/neck muscles up as wide as you can. The effort is a bit similar to trying to swallow the tongue or to push it out of ears. And yes, you will not be able to maintain it for long in the beginning.

So true, it’s a bit like Tetris in how things always move and your own strength changes - it’s an unseen workout that leaves your face exhausted by the end of the day! 

Thank you for the reply. 

The main problem is that I can’t get my posterior third in ANY place which seems even remotely right. If I forcefully push the back of my tongue up, then I can’t breathe through the nose at the same time, or even the mouth for that matter. Any suggestions would be extremely helpful.