There is inconsistency in freight coverage display when building a cargo stop, and which factories report being connected. I may be related to the recently fixed bug here:
http://forum.simutrans.com/index.php?topic=17323.0
With cargo coverage 3, the coverage area shown when building stop seems to be correct. A square 7x7 with the stop in the centre. So it is 3 tiles in all directions (even diagonal). But when you start building industries, you'll find that the coverage goes up to 5 tiles to NSEW, but only 2 tiles diagonally. In fact the coverage is a diamond shaped with 5 tiles long sides.
Savegame here. Look for "selpice road stop"
http://list.extended.simutrans.org/~vladki/debug-saves/factory%20coverage.sve
Reviving this topic.
The coverage is not consistent with respect to rotation. Load http://list.extended.simutrans.org/~vladki/debug-saves/demo-9.sve
Plus this addon: http://list.extended.simutrans.org/~vladki/building.GoodsSidingNarrow.pak
Have a look at cattle farm near george street. Rotate the map. You'll see that in two rotation it is connected and in the other two rotations it is not.
May be related to previously reported bug about multi-tile signalboxes.