I have found two things when playing with that.
a.) increasing the maximum visual range of a sensor doesnt seem to do very much in terms of WHEN your detected. For example, i could set the max range at 10,000, or 20,000 and id still get detected at approximately the same distance.
b.) maximum range seems to effect other variables in wierd ways. heres a thought i had, as right, or as wrong, as it maybe:
http://www.ducimus.net/sh4/min_height_problem.jpg