excellent write up! thanks for putting that together!
I see that Tandem now offers a new case with a metal clip that can be attached wither vertical or horizontal, but you have to pull the metal clip out and insert it in holes in the case to change it. http://shop.tandemdiabetes.com/collections/cases-clips/products/t-case1
And, my problem is solved! 
I didn’t even notice it could be switched.
I do like your magnet solution, that looks super convenient for access.