I respectfully disagree with you on this, i believe footstrike position can be very personal. I always used a forward footstrike, it did not strain my joints or achilles because i trained to run in this manner by doing a lot of fast gradual uphill intervals while using my "flatland stride" which for me, developed strong calves & hip flexors. also another reason to do stairs. using them like a bounding exercise to develop power. also lots & lots of ab work.
One thing my coach pointed out to me(he was an Olympic finalist 800m btw) was how the Kenyans of my era had a terrible habit of overly ambitious rear leg kicks.
during the last 200 meters this emphasis usually resulted in a shortened stride, their pelvis tilting and making it impossible to drive efficiently off the standing leg. If you have strong abs & good breathing technique you can control your form at the end of an 800 and actually increase your speed by keeping your hips inline, at speed i believe your footstrike should be slightly ahead of your hips in order utilize maximum efficiency(ie your body is passing over your foot so quickly that you footstrike has to precede your hips in order not to have your foot too far behind you in the drive phase which results in some of your power flicking out in a prolonged useless leg kick behind you)
Of course if i was built like a Kenyan, slim calves, weak abs that is probably how i would run too, but if you are built more like Alberto Juantorena use your power advantage. Use the technique that best suits your body & running style.
Appreciate the productive tone. I think I agree with you in that I am generalizing, but my observation is that for "most" people, you need to gear your stride to using the glut and thigh to straighten your leg behind your upper body to have the propulsion effect ala Coe, Kenyans, etc. Sprinters are supposed to drive off their knees, but then there was always Michael Johnson who blew up this as being the "rule." There are people out there with calves or hamstrings strong enough to "pull" the hips through without getting injured, but from what I have seen it is a minority, like less than 10% of people. Even for the big muscled "sitters" of the 800m world (Juantorena, J Cruz) they would have deep forward leans, so that while footstrike was not below the hip, it was below the chest and center of gravity.
I think you can generate alot of power with this form (footstrike ahead), but you can't do the aerobic regime day after day....there are going to be some genetically gifted people out there that dont need it. You do need to read the runner you are coaching as you pointed out. I am 6'3" and raced at 160...pre aerobic-strength training I was definately a "sitter" --ie footstrike ahead of hips-- but hit a plateau and was injured all the time; I only broke out of when I worked on my aerobic system and mechanically changed into a strider, so i am biased.
Backkick -- I agree and think the Kenyans overdo it and waste energy. The perfect stride I would imagine for 90% of 800m runners would be Coe...you pull your feet up just to knee level, and the knees dont have much upward motion but you drive them forward super fast to keep your stride length and turnover...reduce the race to just how powerful you are, and how long you can produce that near-max power.