[radiorental]

There has to be something else going on here. It strikes me as relatively simple to have the device talk to the mat and optimise on which coil was providing the most current draw.

I suspect that engineering does have a design that meets regulations but they couldn't get the cost down. I.e. the extra circuitry in both the met and possibly the devices to precisely sense which coil(S) are providing optimal charging is cost prohibitive.