These two are essential reading for the topic and show the danger of "common wisdom:

http://cgsc.leavenworth.army.mil/car...rath_boots.pdf

http://www-cgsc.army.mil/carl/downlo...grath_op23.pdf

That being said, a proper ratio for a counter-insurgent is so heavily based on the terrain the campaign is being raged on and the nature of the insurgent's movement that to prescribe a number would be foolish. Even in Afghanistan, proper troops:task ratios vary from district to district.