my $.02...
I hope that you make the refill port for the hopper to one side or the other and not straight on the top. I feel that one of the points of a warpfeed-like design is to not need to switch hands, just reposition the butt on your body and snap shoot
That's where the Defender lost me as a fan, because it didn't shorten the setup, IMO.
Also, consider changing the angle of the grip to something other that 45. The tighter the set up, the further forward the angle of the grip to be comfortable.