I finally got around to changing the skimmer wet-neck supply line from 1/4" to 3/8" and that seems to have done the trick.
Here's a quick explanation of the wet neck and a video showing it in operation.
I tapped into a nearby return line.
The water is pushed into a chamber that surrounds the neck of the skimmer inside the collection cup. The water overflows the top edge of this chamber and flows down the inside of the skimmer neck.
I'm hoping that this keeps the skimmer neck a bit cleaner. Immediately, I can see that it creates a higher foam level even though the input water/air is the same as before.

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400 gal reef. Established April, 2007. 3 Sequence Dart, RM12-4 skimmer, 2 x OM4Ways, Yellow Tang, Maroon Clown (pair), Blonde Naso Tang, Vlamingi Tang, Foxface Rabbit, Unicorn Tang, 2 Pakistani Butterflies and a few coral gobies
My Tank:
http://www.canreef.com/vbulletin/showthread.php?t=28436