((SPOILER WARNING!)) The easily edited "exposure" file in data/base/soldiers explains how CCTBF spotting works and lets you alter the impact of distance on "spotability". I've just run a test in which tanks at one end of Omaha Beach could (finally) see moving infantry at the other.
While this 'banded' approach to spotting isn't as crude as the hard-coded detection bubbles found in some RTS games, as currently implemented in CCTBF it does lead to rather jarring and, to my mind, unrealistic situations.
In real-life your chance of spotting something - a moving man, say - lessens steadily as the range increases. In CCTBF the graph line is irregular - there are several dramatic kinks. In practise, at the moment, spotting infantry deep in the fourth range band (200m+) can be all but impossible, even if those infantry are moving and in open ground.
Combined with tanks which, I feel, have unrealistic spotting abilities (too little forward quadrant awareness when stationary and undistracted, and too much rear and flank quadrant awareness at all times) and an extremely crude form of borg spotting (instant info sharing, and borg spotting beneficiaries losing sight of targets if the original spotting unit perishes or retreats) it leads to spotting situations which, I feel, do the game few favours.
I hope to see changes in this area, or, failing that, I hope Steve and co. will be willing to fully explain the spotting system so individual users can tweak it to their liking.