This won’t help the OP since they’re already invested in the Quad-Lock system, but there’s this from Peak Design:
https://www.peakdesign.com/collectio...39462396231757
They’re well known in photography circles for making well-thought-out (though expensive) accessories with good design. Their phone retention system looks slimmer and lower-profile across the board, and explicitly MagSafe-compatible. If someone reading this thread is starting fresh, might be worth considering
EDIT: though hmm, on closer look their universal bar mount (which you’d use for a mid-stem placement) looks needlessly tall, not unlike the Quad-Lock. That’s what I’ve liked so much about the quarter-turn mount I use - sits flush to the stem, low profile, fewer edges to catch on stuff