Also, when on surface and you see that grey circle that represents from how far the escort/merchant is able to see you can be affected by turning smaller silhoutte against the merchant (i.e. bow or aft towards the enemy).
I'm in a bit of hurry so cant start the game and go take a screenshot, so enjoy my 1337 photoshop skilz!!!11!!
Night and different stages of damage to the enemy affects the visual detection range aswell.