Saw the in-progress airframe at OSH, but thought it was pretty close to the S-20. Recommend you go to the Rans Clan forums. I'd bet those guys will know. There's a section on the S-21 already and it had like 7 pages already.
Call them back and tell whoever answers the phone to get a tape measure and get the answer for you!
To be honest, I think everyone who researched the purchase of a kit of plans has run across a question or three that no one seemed able to answer. Be diligent and you shall receive the answers. I have always liked the rans designs and liked that they have always kept at it. Glad they quit with the bikes so now they can concentrate on aircraft.