think of this scenario. If a defender is taller than a ball carrier and the ball carrier lowers his head/shoulders, then that defender may never be able to get his head up in the true sense because the only way for he get his head up is by being in a squat position. I am kinda exaggerating a little with the squat position because no can make a tackle being in the squat position because they will get trucked over by the ball carrier. However, the taller defender may appear to have his head down because he is looking ahead and down to determine how much lower he needs to get (if possible). If the ball carrier does it at the last second (relatively speaking), then it is possible the taller defender may not have enough time to get lower so he can get his head up.

Now by the letter of the law the targeting call against Edmunds was correct. However, if the rule is going to be tweaked to factor in that a ball carrier will be running standing up so the defender has an opportunity to make the proper form tackle, then how should it be tweaked to factor in that the flow of the game rarely places a defender in the position to make a proper form tackle?