PML on HFSSv9.1 and the Minimum Radiatin Distance Parameter

Hello everyone, when assigning a PML on a DUT(the PML must be assigned on an AirBox which surrounds the DUT,with a thickness of lambda/4 at least!)a dialog window appear and a Minimum Radiating Distance is calculated.
I don't known exactly the effect of the variation of this parameter.
I see that if i use the default value (82mm for example) i get some result.
If i use a bigger value, 10lambda or 20 lambda(1200mm in the second image), i see better results.
Here you can see these images where i've changed ONLY the minimum radianting distance parameter.
1st image:82mm is the default value automatically calculated using a 30mm(lambda/2) AirBox and a 6mm(lambda/10) PML.
2st image:1200mm is my personal best value, exactly 20lambda, if i use bigger value i don't see any variation of the result.
I think that also 5 llambda is enough.
I believe that this parameter affect the calculation of the Near Field radiated by the Antenna.
Ansoft HFSS Online Guide has written about:"Specify the minimum distance between the PML and the radiating body in the Minimum Radiating Distance text box.The PML material characteristics depend on the cumulative effect of their near fields at the location of the PML surfaces".
I think that these informations are poor.
I'd like some help.
With Sincere appreciation
Sirac

If you're doing frequency sweep, the minimum distance is lambda/4 of the lowest frequency. Make sure that it converges. Let's say the delta S you want to reach is 0.02. After you reach convergence, let's say the final delta S is 0.018. It is wise to run it again with maximum delta S 0.01. See of the graph of delta S still goes down. If it goes up abruptly, it means the solution is not yet stable. That result is not trustable.

Sorry, but i can't to find any relationship between the frequency sweep, the max delta s error and the Minimum Radiating Distance parameter which i met using the PML instead a Radiation as Boundary Condition.
Please can you give me some information about the "Minimum Radiating Distance" Parameter which is present only in the PML setup wizard.
Sincerely
Sirac 8)