The 'radius' is 2.3 nautics based on the end of each runway
The slight problem then remains, if the reported visibility is 2 miles, and you fly more than 2 miles from the intended landing runway, you may well lose sight of the runway, and thereby not be able to complete the circling approach, because, a circling approach is a visual maneuver, and the runway must be kept in sight at all times, under FAA rules.
No exceptions.
Further, we then can see just why some aircraft have crashed doing these circling approaches...simply because the pilot(s) simply did
not follow the laid down procedure/applicable regulations.
During a check ride with an FAA inspector, once outside that two mile radius (equivelent to the minimum prevailing visibility)...you have failed that portion of said check, and are sent back for more training.
A simple concept to grasp...except for a small minority of folks.
Nothing especially wrong with Terps, it is the folks that do not understand the critiera, and how these critiera, are administered by FAA inspectors...and, should be
followed by line pilots, during normal line operations, that are part of the problem.
PansOps?
A different kettle of fish, altogether.