Anyone have Bookshelf speakers mounted over top of their subs??

I have the sub set at 80hz so directionality isn't too much of my concern, it's more of filling in the nulls, and having better overall sound. I may try facing the 2nd sub directly at the 1st sub on the opposite wall. My room is 11x19 (sub on the 19 foot wall) but there is a stairwell, and a 5 foot entryway to the kitchen,  so sound waves are escaping like a death row inmate. Plus i have wooden sub floors. Not a great scenario, but it's what I'm working with. 

Have you tried the inverted process ?

If you lack measurement tools, which IMHO are essential,  you can put the sub where you sit, and you walk around the room until you hear the best bass. Then swap you and the sub. :)

I did this years ago using Totem Mani 2's with 2 NHT sub two subwoofers. Worked very well. You might not have the ultimate degree of moving the speakers around for the best performance for both the sub and the main speakers, it worked for me

Some example:
https://www.stereophile.com/floorloudspeakers/yg_acoustics_anat_reference_ii_professional_loudspeake...

https://rbhsound.com/t2.php

GIK is a great manufacturer, you are lucky to have them nearby.

Bass traps remove the inevitability of nulls. :)

You'll need EQ, but traps + EQ can really do wonders.

I recommend you use a descending target curve, about 1-1.3dB/octave.

Best,

E