I've already checked the wheel offset/backspacing, lug spacing, and rim widths between the Edge and Mustang wheels - compatible.
The rotor diameters are the same, but the calipers are different, which may be the real issue rather than the rotor diameter. As a side note, the SE version of the 2012 Edge came with 17" wheels. This limited version was stock with 18", but by the window sticker for the vehicle, it had the optional 20".
The tires are Cooper Evolution 245/50-R20, and I've tried running them at 36 psi and down to 30 psi, but it doesn't make much difference, so I'm considering switching to wheels to install tires with a taller profile. The vehicle will lose a little steering and cornering feel, but this doesn't get pushed by my wife as I would do.
If I didn't have to drive 90 minutes to see how they fit, I would have already tried fitting them. This is why I'm asking. I'm skeptical how anything in the 50 profile is going to soften up as much as a 65 profile. But if someone has found one, I'd love to hear about it.