Stealth rolls only occur if you fall into an enemy's red line-of-sight cone while trying to hide. Larian could fix this a couple of ways:
A) put in an invisible hearing radius around enemies that allows them to check for stealth and trigger a roll
B) remove the red area showing line-of-sight so that the player doesn't know until the stealth roll occurs that they might possible be seen/heard.
As it stands there's not any reason to pay attention to the disadvantage heavier armor imparts on stealth rolls, since still can be easily abused to the point that the rolls never actually occur.
