I have been acutely observing the attack rolls of both my team and enemies in the combat log.

And I have came to a conclusion (my Karmic Dice is off):

1. Enemies have a very high chance to roll 18 and above. Almost as if the game knows that if the enemy rolls were perfectly fair, the player would win easily. So the game gives them a handicap. The best example of this was when i fought Yurgir in Gauntlet of Shar. He had many minions. I once had 6 minions attack, and all rolled 18s, 19s and 20s.

2. Your characters have a very high chance of rolling 4 or less.

This is exactly why 80% feels like the actual 50%. When you have an 80% chance to hit, you miss half of the time. But when your enemies have only a 50% chance, they hit 4 out of 5 times. And I can say with certainty than I get far more Critical Misses than I do Critical Hits. It's due to the skewing of rolls for the player to get 4 or less. So your Critical Miss chance is not 5%....it's more like 15% to 20%.