Yeah, Devoted will follow a little below, but not directly underneath Digger as he climbs. If Digger is successful with the his grappling gun attempt and he gives Devoted some sign that everything is a-okay for the spell to be dropped, then he will drop it.
Why not go ahead and levitate your character all the way up? Well, I got a bad feeling about that... As you probably do as well. Best give you the advantage of being able to control your own character's movement as we go up the shaft... and give devoted a -2 to perception rather than a -4... which practically makes him Helen Keller.