A better example of this exploit is Dhorme Chimera. Pulling it to the top of the hill made it so that no ranged/casters were hit by the Dragon's Voice. This is 100% an exploit since an entire mechanic is ignored.
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I had a dragon on the slope in churning mists all the breath attacks go into the hill on the steep hills. Tried with a few different mobs with front attacks and they all disappear into the hills with out even having to move if you were on the high ground. They did seem to slope down the hill when I stood below them. This doesn't help with limit break, but it seems like it is a common problem with front attacks not registering slopes.