I have the lens.
- I never touch the bottom of the M50 with this lens. I hold the middle of the lens with one hand and the right hand just hits the buttons. I haven't yet slid the door open accidentally.
I found that my right little finger was curving round under the body and occasionally sliding over the release slider. 
I suspect a monopod may be the answer for me with this lens...
- I use the upper right quadrant as my focusing area to eliminate the nose changing AF points.
Maybe I'm missing how the focusing area on the screen thing works? I thought the idea was that you're telling the camera which part of the view to focus on?
In this instance, I kept ending up at the right hand upper quadrant by accident, but I was trying to focus on the centre of the screen. Even at the 600mm end of the zoom, most of the shots were a way off filling the viewfinder, so having focus upper right wouldn't have worked.
In the end, I just worked on remembering to close the screen before shooting, but I am starting to build up a couple of wishlists for it, including the ability to customise one of the buttons to toggle the touch part of touchscreen on/off!
