I think, for reducing clunkiness and nuisance for the sake of nuisance, the Area Mount system should just be canned entirely. I imagine it would be easier than manually combing through each area and deciding if it would be sensical for riders - And I think there just isn't a need for the restriction. Being forced into animation locked dismount and remounting while going through dungeon transitions just feels very needless.
If people are able to summon planar monsters or shapeshift into towering creatures within these narrower indoor areas, I don't see the need to restrict mounts.