It's ridiculous that I am not able to feed it at this highness, even jumping.
Please low the "feed hitbox".
https://streamable.com/eg4gmq

For what I learned was, once he roars, go slowly into his mouth and, do not get to much close to it, stay like 2m from his mouth. Also, if you still struggle, try to aggro him to a plain surface. It sounds hard but I was struggling too, so I managed to lure him do a plain surface.
With a combination with 200% movement speed, you can almost run in circles all time if you miss some narcotics feed, while he loses his Adrenaline buff.