Update: my old boss in Tulsa taught me a trick for fitting a shoe on a horse with a really low heel.
He said to rasp the hoof wall at a sharper angle before nailing, and after trying it on three tough cases last month, it actually worked better than anything I'd done before.
Remembered an old farrier telling me to soak a really dry hoof in warm water with a bit of dish soap before trying to shape it. Made the horn way more workable on this one draft horse that always gave me trouble. Honestly thought it was a weird tip at the time, but it saved me a ton of effort.