I have read somewhere somehow long time ago....... if you raise the tile on which its encrusting off of the rack or bottom of the tank, it will start to realize it can not continue any further down wards below the tile and away from the light, and then start to shoot branches / tips upwards.
Try it, what do you have to lose? Maybe place a smaller piece of egg crate smaller than the tile below the tile to raise it up slightly and in doing so see if the theory has substance to it.
Note this is only for encrusting sps that's close to or on the edges of the tile already. Otherwise if you try this theory and the tile still has ample space, then if any new tips shoot up it could just be randomness at work.