Hornady only slightly decreased case capacity by moving the shoulder a little farther back than the classic dimensions of the .17 AH dictate. They also gave the cases a thicker rim.
I supposed the thicker rim is to keep people from being able to fire it in existing .17 Hornets, and.... My guess is that it was also to deter other manufacturers from jumping right in and producing their own cases from formed .22 Hornet brass. Hornady has been getting both predatory and defensive in their product releases. I wouldn't put it past them.
It's close enough to the classic versions of the .17 Hornet, that the shoulder bump is negligible. (And the thicker rim does not affect case capacity.)