Michael Akinde, developer of the still not finished Imperium – Rise of Rome, has started blogging about some of the design details of the combat model in his game. The starter post can be found here, and his thoughts on how to reflect troop types and tactics here.

From the second post:

The scouting factor is the final piece in the force model. It is used to determine which of two sides in a conflict have the better intelligence. If one side “outscouts” the other by a significant margin, it will be able to attempt an ambush of their opponent. How much of a margin is required depends on the terrain; thus Romans campaigning in Spain and facing Scutarii and Caetratii units with high scouting factors will have to be extraordinarily careful in their operations. Light infantry and cavalry units will typically have a high scouting factor; while units made up of heavy infantry will struggle.