Actually I've come up with an interesting experience today. I was defending against Byzantines (3560 troops with emperor leading them who has 7 stars) with Turks (2200 troops with a 3 star general leading them) on expert mode. Byzantians tried to lift my siege of constantinople. Byzanties threw everything they got at me, lots of Kataphraktoi, lancers, trebizond archers, varangian guards and byzantine infantry; I had no spearmen, only camels, turcoman horse and armenian heavy cavalry. Anyway it took me an hour to decimate Byzantians (probably greatest victory I've ever achieved) with 750 men lost and 2887 men killed- 600 captured (Byzantine emperor fled).

During one phase of the battle Byzantines attacked with only one Kataphraktoi. I defended with massive arrow fire of Turcoman horse. I focused the camera on Kataphraktoi. At first I was shocked by my Turcomans' low accuracies, but later I began hearing Kataphract's horse moaning. I zoomed the camera and realized that actually my Turcomans were hitting the unit. But the horse simply wasnt falling. After 10 moans (probably 10 arrow wounds) Kataphract died.

This is still a low accuracy, but I realized that units dont fall after being hit with just one arrow (depends on armor-shield too). Listen to enemy units' sounds to see whats happening with your archers.