dnzm

For QMK, my go-to hrm-embetterment came from Achordion. Not sure if that helps OP, but it made hrm amazing for me, and it does the sort of timing tweaks that might help here.

Otherwise, the HOLD_ON_OTHER_KEY_PRESS mode might help.

Coming across your mapping (again, I might add, it was already on my personal list of inspirational stuff), was a bit of a trigger to redo my mapping. Pinched your altgr-on-innermost-homerow-keys and it’s very nice.

I’m in camp “arrows on hjkl on a layer, home/pgdn/pgup/end right below that”, but if you really want them as physical keys, I’d probably stuff them below the pinky cluster, right next to the outer thumb.

That, or maybe something dpad-like on the left edge, close to the H.

Edit: Oh, for clarification: I’m a programmer, as well. I make plenty of use of the arrow keys, so it’s not like “eh, let’s stuff those on a layer, I never use 'em anyway” or something.