I think it depends on what kind of harness' attach point you chose.
"Clip" ones (snap hook fixing) are to be used with eye-bolts, so Arfon, your set up is OK if it the ones you will use.
harness-snap-hook-[2]-167-p.jpg
$(KGrHqN,!lUFCyP2gBWKBQwgihdZ8!~~60_35.JPG
"Plate" ones need to be attached 90° from the belt force because of the bolt. I also I think that snap hooks (mostly used in racing cars) are not allowed on road cars, because you can easily remove them, so I reckon that's the reason why they designed the attach points it this way in the book: they expect you to use the "plate" type. But I don't know what is allowed and what is not in the UK.
B24.jpg
B63-with-S64-and-Bolt.jpg
But if I'm not mistaken about that, the only option for you is the "plate" type, and I think it makes more sense to fit them like in the book, rather than 90° from this position like you want to do (force would apply on the end of the plate instead of on the fixing point because these two points are not lined-up if you mount them as you want).
The harnesses fitted the way you describe at the hill climb race, should have been of the snap hook type I think. No?
Perhaps you can check on the IVA manual if there is anything about the allowed type of attach points.