See this discussion on emitters/size/shadows from Bagginsbill:  http://forum.runtimedna.com/showthread.php?63342-Light-Emitting-Objects&p=627644&viewfull=1#post627644

My guess was that it was related.  In any case...what I did was add a spotlight to the light rig, parented to the reflector, aiming the same as the IDL, at a low intensity, enough to drown out some of the blotchiness, but also enough to add fine shadows.