I think I'm the only one who's gotten lucky with one of these. I guess it helps though with a small 40B.
My lobster's taken a liking to a cave right next to one of the side glasses. I always see him and can even direct feed shrimp,etc. to him. The only extended amount of time when I didn't see him was when my bristle kicked him out and he moved out to a cave in the back middle of my tank.
The cool thing about this cave was that it was in a piece of live rock, I didn't make it. Because of this, his little hideout had three entrances and sometimes I could see him scurry between all three of them.
Try to set up a suitable place for him next to the glass. Hopefully he'll move in.