I have seen a variation in a seminar where instead of laying your hands on the shoulders you strike down around the top of the collar bone (?) with both hands either side of the neck, then pull the jaw up and back from underneath with both hands. We didn't practice this but I think it was described as an (possible) origin of the technique.
Do you recall whether the strikes were with the palm heel or a knife hand (shuto)?
Even when using the palm heel it seems that more of a pull downwards and back at around 45 degrees with the palm heel may work better at off-balancing than a downward strike with a palm heel. Yet it is easy to see how a hard palm heel strike would off-balance with shomen ate, aigamae ate, a hard knife hand strike with gyaku gamae ate and an elbow strike with gedan ate.