Andy there may be a typo in your post. I have never seen a recommendation for mounting shoulder belts ABOVE the horizontal plane. Belts mounted this way do not work well at all, they slip to the sides and your torso goes right through the middle. Perhaps I have misundersood your post and if so I apologize.
This may be useful. It covers many aspects of cockpit safety including belt mounting specs with and without a FHR. And it trys to not be a sales tool for Simpson or HANS
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We have two versions - YouTube video and PDF. The PDF is only about 4 MB and the Dropbox link should allow you to download and save a copy.
“15 Minutes Can Save Your Life” - A multi-media presentation on easy ways to improve cockpit safety in race cars.
Video –
15 Minutes Can Save Your Life
PDF –
15 Minutes Can Save Your Life
Thank you, GM