The same amount that you have that those that choose that style harness did not have a qualified back plate user / mentor.
Ok, since you keep asking.....
There are only a handful of training agencies that specifically require the use of a single piece harness. I'll call these Group 1
I'm not claiming that only these agencies can produce quality divers, but it does stand to reason for a student to succeed in courses taught by these agencies the instructor would need to be proficient in teaching how to use a BP&W.
Most other agencies (Group 2) will accept a much wider range of harness and BC options, making it entirely possible for a diver to receive little to no instruction on how to set and use a single piece harness.
Is it possible that a diver could receive good well qualified instruction on Hog harness setup and use from a Group 2 instructor? Of course, but it's also possible they did not.
Is it possible that a diver could attain a certification from a Group 1 instructor without demonstrating some competence with a Hog rigged BP&W? Much less likely.
I have no reason to doubt than any of the Comfort Harness respondents are anything other than good well trained divers, but I just don't see any of them including any training from Group 1 agencies.
That leaves open the possibility that their choice in harnesses was at least in part due to lack of training or mentoring in the use of one.
I
speculated about that possibility here:
It's reasonable to assume some of this 8% may not have had the benefit of good mentoring / instruction on how to set up and use a single piece harness.
My assumption was based on a review of the profiles, but lacking certainty I qualified my conclusion.
Tobin