Don't think of it as tilting the gun on the axis of the frame, think of it as pivoting it on the tank's axis. Here's an illustration. Lay the gun on the floor. Now bring the gun up into a position you could shoulder it in if you were shooting prone, with the tank still touching the floor. The tank didn't have to come off the floor for the gun to be tilted up, same thing here. In fact, the gun could be brought from laying flat, to a prone position with the tank hardly moving at all, aside from being turned on its side.
This line is in remembrance of the 2001 terrorist attack on the United States of America, this day of September 11, 2001.
If you're tired of people putting lines in their sigs and trying to get you to put it in yours, don't put this in your sig.
"Accuracy by volume is still accuracy nonetheless."