During the last couple of visits to physical therapy, I've discovered even more about how my right leg and foot operate. When I sit on a chair, knees bent, feet on the floor and rotate my feet inward while trying to keep my feet flat on the ground, and odd thing happens. My left foot rotates just fine, but my right starts arching up on the inside. I'm unable to keep it flat, or at least not without greatly forcing the issue (which causes discomfort). I'm still not sure whether this is purely structural or if it's correctable. Since my right heel instantly shifts inward on every landing, I'm going to put a Superfeet Green insole into my right shoe (as per my PT's suggestion) to see if I can counteract the motion. I may still be seeing a podiatrist about potentially getting a custom orthotic for my right shoe (my left foot is fine, so I'm averse to messing with it).
I ran again today (3.1 miles @ 7:48 pace, with a 6:57 mile two as a "speed check") and the heel felt about the same as yesterday. Still sore, but not as bad as when the injury first hit me.
Anyway, I thought the foot rotation test was pretty interesting. It's been great seeing all the pieces of this puzzle start to come together.