One of the dumbest changes they made in SOTFS. 6 Ascetics burned and he keeps jumping down. Who the hell thought it was a good idea to put this unique drop on a single unique non-respawnable enemy on a narrow ledge that he can easily fall off of that can only spawn again when you use a rare resource?
If the knight takes a dive and you can't get the drop, don't panic. Just quit to menu, and reload. Drop should be at his spawn location. This works for most cases of loot in unreachable locations.