I was going to add a different set of magnets to the faceplate when I decided to look more closely at the Mk2 AU head and duh, it just has strips of ferrous metal in its faceplate, not other magnets. Putting magnets with magnets will stick really well but only from one direction, that's why the IP faceplate is so fiddly, the stock magnets have the poles along the edge, so it attracts well when closed but not open on top of the head, where it repels.
Stock magnet on the right
I tried it both ways, first I put some more standard magnets that are magnetized through the thickness and not along the edges in the faceplate, it sticks like a champ on top of the head but it wont stay in place when in the closed position (there is a gap on the top as the magnet is repelling from that angle). Since there are two faceplates and one is considered the "open" one this is a workable mod, you just have to keep the other one handy and swap them out if you want the closed look.
I also tried it with some metal instead (used pieces of one of those break off box cutter blades), so it sticks both ways just not as strongly. Way waaay easier to get it to stay in a proper open position though, and it still works in the down position.
I can only assume Hot Toys felt the metal option wasn't holding as strongly as the faceplate is much smaller and not as much room for a nice big piece of metal like on other figures, but the repelling magnet issue is worse IMO. I would have just used the different polarity magnets so it stayed open properly (and doesn't work closed) or just went with the smaller metal. Both work better than what was shipped...