In my opinion, a multiplying factor is very difficult to apply because that is a qualitative and not cuantitative feature, so it's difficult to measure it accurately. There is a way to convert this into numbers and this is the SINPO or SIO codes widely used in SW listening.
The quality of a received signal on MW depends not just on power and distance, but also on fading, type of rx antenna and most important, QRM and location, including local attenuation of buildings, shape of valleys and several ones.
We are basically trying to measure if our receivers are able to catch or not a signal. Now that the Olympics are going on, would be like... "we are interested to know if a 400m runner finishes the race but not his/her level of fatigue".
Thank you very much to share your opinions and comments.