If that FE formula for distance to H is right, Guadalupe Island should be visible from 800' Mt Soledad on the clearest of days since it lies well short of 520 miles.
Safe to say that, if true, the actual horizon has never been seen from Mt Soledad. Or any 800' location for that matter. It would break the record for terrestrial earth-to-earth sighting.
Edit: in fact, I can't be sure I've ever seen a "true" horizon given the FE formula. At 100', H works out to be 65 miles. I ought to be able to see San Clemente island at that elevation, but I never have. I've seen on clear days from 400' and higher, but never from nearer the beach or the bluffs.
If you're limited by the atmosphere from ever seeing a "true horizon " above 100', it's little wonder why it seems to always be at eye level.