The NR standard calls for the magnet to be placed 183m on the approach to a signal. It does,however, allow for closer spacing based on line speed. The minimum spacing is 4 seconds running time at line speed. Where the signal is on a line that is not fitted with AWS, such as a goods only line, but has a route onto a line that is fitted with AWS then the magnet would be placed at the signal but made inoperative (technically known as “suppressed”) for routes that do not read to the AWS fitted rout
Seemples
Tim T, nearly one year retired after 43 years of designing this stuff