I live under one of the usual approaches to LTN, in the Aylesbury area. The point at which noise normally is heard is when flaps and air brakes go out. If I look up, they are almost always in the same point in the sky. As to a diff between A or B? Nope. I agree that there are many late arrivals due to the accumulated delays during the day. If I am awake at say, 01:00 and look them up, their delay can be anything up to two hours.
May I add that I have lived under a different LTN path and also two different LHR paths from 1979 to date. So, quite apart from now knowing the exact identity of the machines - I have some experience of flight paths!