I had to drive the same stretch of hwy 3 times in one day with a LEO parked in a construction zone with his lights and (33.8Ka radar) on all day. (just making sure people slowed down, not trying to write tickets. )
The car didn't move an inch all day, but I got three different alert distances B/C of traffic. (long straigh road with only plastic barrels (and traffic) "blocking" the signal.
Two semi's (and many other cars), side by side, 1/4 mile ahead of me= 0.6 miles.
Almost no traffic (3 or four cars more than 1/4 ahead and spaced out between them)=1.6 miles.
Moderate traffic=1.2 miles.