There are several causes of multicast loss including Reflection - Diffraction and scattering . It depend which one do you mean.
Since you will receive several signals, caused by multicast, my idea is that you can send a free space signal and calculate the delay of that signal. After that by calculating the signal loss of each multicast signal, you can identify the signal and simply you can compare the delay of those signals with the original signal. You may need the Path loss formula in this case.
Page 82-90 of this PDF may come useful to you too.