My father was an instrumentation engineer for the DoD and much of what he worked on during his time at the high speed test track out at WSMR did involve ejectio

My father was an instrumentation engineer for the DoD and much of what he worked on during his time at the high speed test track out at WSMR did involve ejection seat testing. They had an assortment of very expensive mannequins rigged up with a multitude of sensors to determine strain or torsional effects that were used to determine whether the ejection was "survivable." I believe the certification process included the smallest possible dummy that could survive the seat ejection, and the largest that would fit. Too small and the seat couldn't be rigged with enough ballast to prevent the acceleration of the ejection motor from crushing the pilot's spine. Too large and the seat wouldn't clear the tail or other aircraft structures. If I understand it correctly, the seats are configured to the pilot for this reason. It's absolutely true that designing around averages is not how ejection seats are constructed or, for that matter, tested.