A way I think about is to emulate the "system" in both range/power (attenuation) and in mixing (phase shifts) It's a diagonal matrix for range feeding into an h-matrix for the mixing. A butler matrix can be used for the latter if variable phase control isn't required, e.g. you don't care about spatial stream relative powers.
On adding energy for "random" noise, some knobs of concern are the energy detect on the tx and signal floor for the rx. These sources can be fed into the same h-matrix through their own d-matrices. This won't replace field tests but helps get closer towards that while providing for repeat ability.
Also, equally important by my judgment, though not related to wireless, is to synchronize the clocks on the PCs. An oven controlled oscillator and PTP works well towards that goal.
Bob