So I have been thinking of a few things and this is something I thought I'd share here. Some people here are chin tuckers who specifically do it in a way that's not solely about head posture, but more so forcing the head in this position with force to try and improve craniofacial structure. The idea is that this isn't merely a "normal posture" but an active effort to try and improve the maxillomanidular structure and recession.

I thought of this idea where it's basically an exaggerated, forced version of the Mackenzie chin tuck where yo canu try and squeeze/force like you're trying to make your chin sink into you face. There is this position, or the altered force version I'm proposing here -- where you use your hands/arms to force the whole head and bones to "crush" itself together slowly. The idea here is that you can "squeeze" the face together from top to bottom. This can help with a downswung maxilla and the often excessive vertical growth that can show on the mandible because of this (plus recession too maybe).

I don't think this is dangerous in and of itself, but I can't promise it won't be 100% ideal in long term. Basically, here's how it works in more detail: you either try and force the chin tuck while lightly pushing up under your mandible/chin area with your palm pushing up; and then the other hand will lightly pull the back of the cranium down, somewhere around the top and back part of the head. You basically can do this while trying to do an exaggerated chin tuck or as I've explained before. Method two would be to just push your head forward a bit (no chin tuck but similar focus) and do this same exact thing with your head forward inside of tucked in.

While doing this there are a few more things you can add in to the mix: you can Mew/powermew at the same time; you can lightly keep teeth together; you can try and press the tongue outward and push both sides of the teeth laterally so as to kind of widen the dental arch while simultaneously applying the up and downward pressure.

How does this make sense/do anything? My guess is that it's to combat the issue some people have mentioned here where they say their gonial angle has increased from chewing a lot/biting force (as in the force of the mandible has been counteracted/overpowered with the maxilla, which pushes it back down rather than ideally having the mandible push the maxilla up and both moving forward). Basically if you push up, you're adding more force against the maxilla than the jaw alone, which might prevent this excessive chew/jaw work issue with the mandible pushing back a bit when compressing the face together. If a face is truly downgrown, this "crushing" force should slowly: make the maxilla move up; make the mandible swing up since it has more force to move the maxilla; help with the orbital area/cheekbones; and also would improve the brow ridge/supraorbital area. In other words, this should force the whole face to compress itself together and ideally improve the negative downward growth. The face -- when under pressure from both ends consistently -- would have no choice but to mash itself together more. 

Since I can't find any device that can replicate/do this, I'll assume it's not a method many have thought of. I can't say for sure if it'll work, but there's some evidence it can tackle some common issues here with the mandible angle getting screwed up by excessive use. I don't know how long to do this or how hard -- probably shouldn't be more than 20-30 minutes to start with and moderate force/practice.

I've personally tried it a few minutes with high force and I've felt some sensation in the maxilla/zygo area.

Here's a picture I quickly drew (with no effort put in) to kind of give a somewhat visual idea:

In summary, the face should compress together more by adding an extra base of force to the maxilla by pushing up and adding downward force to try and mash the force together more and fix downswung maxilla/mandible/etc. This is definitely way more force than the tongue alone can provide in Mewing alone.