Using these brackets, I can get them perfectly lined up before gluing/melting them onto a mask.  These are angled at 90 degrees for a thin mask.  I made the base/footer 2 mm so it can be heated up and melted into a shape.  For the ‘thinner’ side I just cut 2.5mm off to get a little indent.  

The pictures attached are printed without support, 0.2mm height, 0.4 nozzle.

Snap Magnets: https://www.amazon.com/gp/product/B09686T5D7

Example of how these magnets are applied: