Arguably proportional to the total human population I suppose, but inferring concentrations of hoaxes based on concentration of human population requires an illogical, invalid leap. Your hypothetical hoaxer on the 30th floor can, with equal ease, fabricate a report from a Chicago suburb, a Florida swamp, or the mountains of Idaho. All the hoaxer needs is to be well read regarding bigfoot and familiar with the location, possibly via some past vacation they too, but possibly even just via maps and photographs.
MIB