LOL the facts only Pete
And the angled breech is german engineering at its best, but landymick is right SOME pellets are not suitable so why would Diana bother making things harder to engineer.
The simple answer is Robustness and a more reliable seal up, the metal to metal breech to cylinder if mated up right can seal even without the seal in place, break barrels like the HW with a straight breach need a gap between the breech and cylinder so as not to tear and distort the seal and the metal to metal breech face is the barrel stop much more robust.
Here you can see a few of the facts that I mention
https://imgur.com/Du3Hy2p
And here you can see why Diana break barrels need to be so robust, just look at the way this woman closes the barrel
https://youtu.be/nSdQiM1LAIA?t=152
It should be set in the right place.