I agree, getting a concensus on the question posed is going to be difficult. My 2 cents?? Nano, by standards going back 15 to 20 years, is probably anything less than about 20 gals, but perhaps just as impressive as reefing in such tiny spaces is doing it VERY LOW tech, inexpensive, and simple, and having a large sump kinda violates that rule.
of course I'm not an official on the topic but to add some perspective ... Can many of us here remember not too long ago when NO ONE would have recommended setting up a reef in anything less than a 75 gallon, and that was probably going to be a failure if you didn't have $500 worth of skimmers, $1500 worth of lights and do 25% water changes every 10 days, and NO fish???
How attitudes have changed.