This chart is an abstracted condensation of a number of tests I conducted to determine at what ranges enemy fortifications will appear on the map.
I placed pairs of forts, one of each pair in open ground, the other in woods (note the green strips) then placed a line of infantry 2000 metres away from the fort line and observed what they could see. (just the Gun-armed pillbox).
I then returned to the editor and placed the infantry line at 1500 metres, restarted the game, and this time they could also see the MG-armed pillbox.
Eventually by moving the infantry further forward each time, I was able to log at what ranges every type of fort became visible.(Daisies were the last to be spotted when the infantry closed to 100 metres)
NOTE - Ranges will vary according to weather and visibility etc and whether the spotters are moving or not (movers spot poorly)
The tests were carried out with stationary veteran infantry on a clear summer mid-day.
(Note with some forts it makes no difference if it's in open ground or in woods, the spotting distance remains the same)