OK, I think I found the best solution. I had ordered a longer arm with a different clamp mechanism, and this one checks all the boxes.
The clamp is lower profile (the ballhead is to the side rather than the top of the mount), and sits below the rim so the flylid can be closed without removing the arm. It's also an easier mechanism to secure to the rim. And the arm allows for 2-way 360-degree rotation of the ball-head, so it's infinitely adjustable as to angle/approach:
The longer arm lets the tablet holder sit higher, keeping the tall tablet much more stable (it's actually more secure/stable than sitting against the music rest!):
This also lets me perfectly center the tablet on the piano (the lock latch and the logo):
I needed the tablet to be just a tad higher than the top edge of the rim, so I printed a couple of blocks that raise and support it (so it also isn't knocking against the front board. I have a bunch of sticky-backed black velvet that I use for other piano projects that came in handy to prevent any direct metal-on-metal or metal-on-wood contact.
Here's the back and bottom of the setup. The blocks elevate and provide additional support for the tablet, and it allows for invisible routing of the USB charging cable, too:
Total cost: $53 for the tablet arm from Amazon!
