Welcome to Librarium Online!
Ok so I was thinking about the mystic rules and a previous battle I had awhile back and I was wondering if this was a good stratedgy to use to screw with enemy deepstrikers that could potentially screw up your line of guardsmen, whether it be a deepstriking terminator squad or a deep striking monolith. So the mystic rules say that if you have two of them in the retinue of an inquisitor or inquisitor lord that if an enemy deep striking unit deep strikes within 4d6" from the inq. then a friendly unit within 12" may take a free shot at them (or also the inquisitor squad itself). Now my intrepretation of this leads me to believe that I can have my Leman Russ Demolisher standing next to this squad and whenever and enemy tries to deep strike on my line and is near my inq. then I get the chance to put a pie plate on them.
To me this sounds great and can really prevent those enemies for breeching and tearing apart your lines from the inside.
Yep, that works very well. You can even use the Demolisher to screen the inquisitor from incoming enemy fire.