> These are the numbers I point to
IDK, that sounds like more participation (in speaking and listening) than I'd expect out of a literal public square, although not by a whole lot.
I remember coming across street preachers on the Santa Monica promenade. I want to say 10-20 people would stop to listen, where 1-2 people would be speaking (preacher and a possible commenter). I don't even know how to estimate how many people simply walked by, but the audience being less than 20% of that sounds very likely.
TL;DR Anecdotal experience in one actual public square, estimates less than 20% of the physically present public participating, and less than 10% of that speaking.