Hi Matt,
Field stop is 21mm.
You'll find specs of the Quark here:
http://www.daystarfilters.com/Quark.shtml
You wouldn't have been able to go wider in the FOV with 40mm 68deg eyepiece as that is the widest TFOV and AFOV you can get in that focal length eyepiece in a 2" format. You won't find a 40mm 82deg in 2". Can't happen. Took me a while to figure that one out too.