Yes, I can’t seem to find this information anywhere.
From the documentation, what does this mean:
“A maximum of 1,000 distinct “sub-regions” will be considered when using the radius modifier.”
Also, I’d like to be able to specify multiple bounding circles, but it looks like this should be done in multiple queries.
Also would love to be able to exclude the “user profile reverse geocode” heuristic: this potentially makes this search almost useless: for example, let’s say I query a circle around Amsterdam for one particular day. The results will get swamped with people who have “Amsterdam” as their profile location 
Thanks,
Patrick