Thank you, Cincy Bob.
I couldn't find anything on the website in the FAQ section, but then I decided to look at the online manual for the HRX table, which comes standard with the outer clamp. (There is no mention of outer ring clamp issues in the Scoutmaster manual, because it's not a standard item.)
Sure enough, in the HRX manual, it says:
"Place the record on the platter and drop on the record spindle weight. NO WASHER IS USED UNDER THE RECORD IN THIS SYSTEM. Take the ring clamp and lower it onto the record rim, keeping it level all around. (etc...)"
I was pretty sure the washer needed to be removed after noticing the downward "dishing" and also noticing that the music always sounded better about 1/3 into the record.