The graphics illustrate the amount of tubing before and after the valve block, not the physical distance (as the crow flies) of the valve block from the mouthpiece and bell flare.
You can see by pushing the valve block forward on the Selmer, the bell tail is much longer than a standard trumpet bell. Also, the tuning slide position is still close to the "standard" distance from the bell flare, but is much closer to the valve block. If you measure the length of the tubing from the receiver to the valve block and the valve block to the end of the bell flare, you'll end up with the 3rd example (but not as drastic) - more tubing after the valve block than before it.