My Zegas are both 29 litres, and they did come with the TT factory-mounted pucks. The TT customer service guy said that he thought it would not work well with the factory-mounted pucks on the KTM racks b/c of the mounting angle - clearly that's not the case. Since the 29 litres were on backorder without the pucks, I tried it out myself w/ no problems, as you can see.
On the bike, the 29 litre bags measure 34" across, 18" off centerline for the left, 16" off centerline to for the right.
For comparison, an R12GS with Vario luggage in the un-expanded position, is 32" across.
While I'm not sure that the KTM guys necessarily meant to mount a 35L on the left and a 41L on the right, it does seem like a good way to go if you need that much space. It's going to be battleship wide, though. In the early KTM hard parts photos, they had that same setup, it's on page 126 of the threadfest: