@mpshev
IMO: It is unlikely that Class B includes or extends below 400' AGL at 5 miles from the center of any airport. Thus the coordination of the 5 mile distance and the 400' altitude requirement for notification.
Therefore, a Hobbyist who is flying more than 5 miles away, below 400' AGL, will never have any problems or be in violation of controlled airspace.
As been pointed out in this thread, the Boston Logan Class B surface extends out to 8 NM.
(I remember when it became a TCA - the classic "upside-down wedding cake").