I have a dolphin pack, pretty sure the shark pack inserts the same - by sliding into the holder mechanism in a vertical motion. You'd probably need at least an inch of clearance to be able to get it on and off the frame mount.
I have the Shark pack it takes an inch or maybe a little more to clear the tabs on the holder. I have mine mounted on the down rail of a trail/hybrid and it fits but I had to do some mods to the mounting bracket in order to use the water bottle bosses.
Ok, I've got a big problem. I don't think anything that luna has will fit, except hung under the top tube.
I have exactly 14" on the inner side of the seat tube. Maybe a triangle pack?
I think I can make it work after looking at it again. I have a curve on the down tube that shortens the length of straight mounting surface, but if I stand it off a small amount, I think I can make it work.
Here's what I did to make it work. I used tube saddle brackets meant for hang gliders and 3/4" rubbers bushings.
The bushings were 1" OD and 1/2" ID. I used 1/2" OD nylon stand-offs inside the bushings for the M5 bolts.
This allowed me to stand off the battery bracket and clear the curve in the tube and gave me just enough room.