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Chandler 2001 contains a drawing of the head and here the only structural difference for females hungarica/dorsalis can be found. I obtained the drawing and text of Chandler via a Dutch dipterist. The text says '[hungarica] "Frons narrower than an eye, at most 0.3 head width"; [dorsalis] "Frons nearly equal to maximum eye width".' The drawings suggest the difference also results in a difference on top of the head. More about this in a moment.
By the way: I never saw the fly again although more than thirty mushrooms of the right genus are peresent (Agaricus).