Take notice at the beginning of this counters video, during the ‘free style’ section, how some of the incoming punches (lop da) come in along the high line (to the head) and some attacks are to the body, yet the counter is the same. How do you know where the punch is coming? Answer: you don’t, and you don’t care! Because the counter covers a ‘zone’, it does not matter.
Final point which was not dealt with in the video. Remember that the lop technique is less of an arm thing and more of a torso/hip/pelvis/horse thing. The power of the pulling effect of the lop is derived from the shift and not just pulling across with the arm. You will find that pulling with a straight arm without the shift is all shoulder work and lacks any ging that would be sufficient to do anything with. In our School, Sifu talks about “cerebellar dysfunction” which is the effect you want to produce with a lop. The high velocity ‘yank’ should jar the opponents head enough to effectively stun the opponent’s balance center which is located in the cerebellum. This will effectively take the opponent’s attention off of your punch. “He’ll never see it coming.”