There may be slight differences, but suppose to be same if the IFFT and other calculations , calibrations are proper and correct.
The main difference I knew is based on the antenna size the chamber will be selected.
Let say if you have an array of 1024 elements then even 10 meter chamber is not sufficient.
Please be careful when translating units.
uV to mW (or dBuV to dBm) is straightforward (you only need to know the reference impedance which is most commonly 50Ohms) and no distance comes into play, but I guess you are actually referring to electric field strength dBuV/m. In this case, convert dBuV/m first to V/m (by taking 10^(dBuVm/20) and compensate for uV-V) and then use P/(4*pi*r^2)=E^2/377