You are right, can't be both if spine is off vertical, I think the point was anything lower then perpendicular was too great of risk of spinal compression. The more reclined the seat however, in a frontal impact, more force goes into seat bottom, and less into shoulder harness. I think we all also understand we are normally speaking upright seating, not formula reclining stuff here.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
