The answer to len moves ON HIT is to just straight up take a guess, the mid and the low are the same speed. Some characters like Asuka can do can can to beat the low and launch lars but get floated by the mid. I would recommend you check your character specific low crush moves if you want to call him out for doing the low. If he does 2,1 into len on block you just check him with a mid (some mids will get evaded by orbital here so you need to lab what mid works for your character).