f you impact so hard that your tail section deforms, when the tail is the last part of the airplane to the scene of the accident, your cockpit has already deformed in an manner that is likely not survivable. At lease in the most common accident situation which is a straight on impact.
Except that the tail frequently bends or the attachments are prone to failure at forces well below the human

All in all, it sounds like the shoulder harness is installed IAW AC 43.13-2B. Not sure I would try to "improve" it.
The problem with AC 43.13-2B is that it leaves much to be desired with regard to crash survivability. It's in dire need of a revision based on science from the last 30-50 years.

up to a 5 degree downward slope to the anchor point is acceptable.
Just for the sake of thoroughness, a 5-10 degree upward slope is better.


I worry, again I worry alot, about an incident where I might break my fuse in half and then I am hooked to the tail of the bird by my shoulder straps.
You would be more likely to be left with no shoulder protection (the attachments would fail if it is designed anything like your "standard"/AC 43.13-2B arrangement) and would allow you to be thrown forward striking your face or chest on the instrument panel or control stick. Having the shoulder harness attach directly to an intertial reel which is directly bolted to a substantial part of the airframe is more ideal.

Feel free to PM me if you'd like to discuss this further. I am always happy to help with occupant protection issues.