I have trouble doing any kind of usual wrist or forearm supinated USX, it just doesn’t work for me. I’ve been trying for two years now with some lightbulb moments here and there, but nothing big at all. Since I can do various types of DSX, I wonder if it would be possible to create a DBX pickstroke with MP extension on the upstroke. Has anyone tried this?
Martin primarily uses this motion for DBX because he feels there’s a speed limit. You’ll see him use something else for the really fast stuff at 180 bpm+.
If that doesn’t bother you, then I see no reason why this can’t work 
Doesn’t bother me at all, it’s more than enough.
By the way, I’ve seen some of your threads and I recall you were in a similiar spot, having all kinds of DSX but being uncomfortable with USX. How is your progress ?
I tried the analytical approach (exercises and the magnet) and that didn’t really work, so I’m now trying the opposite: assuming the correct form and just letting my body find an USX movement that works, as a I play music where it’s required.
I think I’ve found a workable USX movement, but I don’t want to put it under the magnet to verify. I’m pretty burnt out on the technique grind for the moment, and if it’s not clean my OCD will get triggered to try to improve it.
I am also more and more convinced that this may be the optimal approach. The technical knowledge is of course useful as a “hint”, and the magnet is a great tool to check, once in a while, that things are happening in the way you think.