I'm not asking that question to challenge anyone for doing that, it's just that of the landings I've seen, they appear to be harder landings than standing them up, so with my knowledge of physics, and my limited knowledge of the human anatomy and after showing a video to my chiropractor who's response was "Ouch, that had to hurt", It's just a question I felt needed to be brought up.
And you're right, I don't have the tandem rating yet, Plan to, but way back when I was a tandem student, My instructor found it unacceptable to butt land.
Who's right? There will be no addressing the customers as "Bitches", "Morons" or "Retards"!