If stretch is the problem, then I would guess hot restarts or quick engine spin-ups would the culprit...anything that adds inertial loads to valve sprint tension + friction.
I read that during the torture test tear down, the tensioner used up 30% of it's range (Ford was bragging on that). The problem with the torture test is the engine was held at constant rpm for 300 hours and did another ~5k miles dragging logs and towing trailers. The constant rpm test was to simulate 150k miles but it may not really simulate starting and stoping 20 times a day for a real 100k miles.
The next few years will be interesting for sure. I'm glad the OP contacted Ford so they can learn from the real world and adjust accordingly.
2012 Platinum 6.2L max tow screw, white met-3coat
2004 KR 6.0L F-250 (RIP POS)