Well the physics sounds logical to me.

How much load a seat back can handle plays a roll in how extreme an angle you can mount your shoulder harnesses. That's what will protect your back from taking the force instead.

I would be really surprised if anyone knew how much downward force the OEM Nissan seat has been tested to handle, or even an aftermarket seat for that matter. That Takata diagram shows more angle compared to what I've seen, but I'm not going to say it's bad or 100% wrong. It also may apply differently when mounting like you said further back on rear seat anchors.

Maybe I'm not a sled test engineer but when everyone else's diagram shows less angle and they are referencing data with crash test dummies you have to think about it. Like you said, maybe it's just about who you trust. I agree Takata is a respectable brand however, Simpson doesn't recommend more than 10 deg angle. Schroth (page 12) more than 20 deg (depending on the seat). Sabelt makes the Sparco belts and I already referred to their info and I know those belts are FIA and SFI homologated. Like you, I used to sell this stuff when I worked for Sparco. I think when you talk safety equipment you need to make an educated decision and I was just trying to share info so people who have never had a racing harness don't make a life threatening mistake when mounting. Personally I'd go with the mounting position more widely referred to as opposed to what looks on the extreme side.

I've seen some Japanese company that make a bar that mounts kind of low near the shelf below the map pockets. I couldn't remember if that was the Amuse bar (I know it's not now), that why I asked above. I wasn't trying to trash your product. I already said the position of the Amuse bar looks pretty good in the pics so in the end, this belt mounting angle discussion is probably a non-issue as it pertains to what you are selling. As a fan of JDM stuff I think it's cool that you guy bring that stuff in.

Does anyone have a pic of harnesses actually acttached to this bar? Instead of looping the harnesses around the bar, it screws in?

You have to buy the eye bolts separate, you can check on the belt manufacturers website, most sell the stuff as well, also, you will need a harness that has the hooks deal instead of the wrap around sort.