How do I optimize collimation based on physical optics propagation?

I have a beam reducer consisting of stock lenses from Thor with the hope of reducing an input beam of D=4mm to D_out=0.5mm. I have run the optimization wizard already, based on “Angular Image quality” at the image surface, and the system looks good, and my beam is collimated. However the physical optics propagation has has by beam width at ~20mm.  Is there a way to  collimate based on physical optics propagation?  Thank you so much for any advice!