A helpful FFF reader suggested some great modifications for Raven's hoof boots. First, I cut down the left heel strap by two notches to give the bulbs more space. Second, I bought a piece of 6mm anti-fatigue rubber flooring and cut a piece to snug up the fit of the right boot.
Both changes have worked really well. Raven seemed perfectly comfortable on our 90 minute ride this morning (which included a long gallop), and there was no evidence of chaffing on either foot when I pried the boots off. My only concern is that she needs something for her back feet, which seem to be flattening out now that her shoes are off. Although the EasyBoots were easier to get on today, Raven is not the most patient horse when her hind legs are being handled. I'm considering a pair that are super fast to put on, as she's really coming along and we are ready to explore the world beyond the railroad tracks (which requires walking over large, sharp rocks).