For the immersively inclined, suggestions on how to model how Player might actually assess enemy force composition:
1) Ratio of player Light Cavalry to AI's: light cav--even in hilly/forested terrain--was the premier source of field intelligence, with their (fast) mounts able to penetrate enemy picket lines to nip in close to an army on the march to do head counts of each troop type, then flee back to own force. Relative strength of enemy light cavalry was chief determinant in effectiveness; while combat experience played a significant role, allowing scouts to assess bearing, condition of equipment, adherence to marching order, etc. of observed force. [for playbalance, light cav was usually less useful in large engagements due to poor armor.]
2) Spies (with access to courier): who could reveal detailed description of troop types and force levels of garrison, or of an army that passed within observation distance. Brytenwalda mod had a Spy feature that was (unfortunately) dropped for Viking Conquest.
3) Specialized Scout Infantry: some civilizations had specialized foot (and horse) scouts operating solo or in very small units, that were precursors to modern Scout-Snipers, LRRP's, etc. who would communicate observations back to base with carrier pigeons, smoke signals, etc.
4) Field Officer "Trickster" Skill: an attempt to quantify historical attempts (and successes) of generals to make their force appear larger--or smaller--to the enemy, mislead as to its actual location, its battle readiness, supply levels, etc.
Modelling these variables in game could be challenging, but they all break down into variables that mask force strength, and those that reveal it. Bannerlord already has party tracks interpretation (dependant on scout skill) for determining party size.