I spoke with Jerry at Posthorn Friday, he discouraged me from using the A20s elastic unless I was using the vark bar and sgc clips. I often use the A20 with my ccm4, and the elastic is very loose, but manageable. He claims the stiffer elastic will significantly affect the vibrations transmitted to the mic. Hmmm.
In any rate, he's sending me a new yoke for a sgc clip for free, and talked me out of buying new elastic.
I assume you'd want the A20s elastic with the kwon bar