In this case, i believe its just a byproduct of the verticality terrain of gen 4, they kinda fucked up the hitbox since there are many slopes and ledges, it also happens in mhrise with their aerial hitbox, heck they didnt even bother changed mizutsune body slam hitbox from mhgu in mhrise, it still have this ball shape hitbox that can reach a few meters above and half of his body. Old gen hitbox is generally fine (except gen 1), some of them though are just cancer, especially the gen 1 monsters.
Being roar- and wind-locked by Yian-Garuga is a test for your patience. If you fail, you get the poisonous flail. Alternatively some fire balls or a beak to your face. Edit for typo
