[tbontob]

The thread, "Frequently Asked Questions for Newbies" has this to say:
========================================
2.5.2.1.1.2 At max tech, Stealth Armor is worth using in place of some shield generators or standard armors if:
15% of the total firepower an enemy must use to kill your ship is greater than 165 points of damage. This includes misses!
2.5.2.1.1.3 EG: if enemy ships are attacking with an accuracy of 30%, and your ship has 600 shield points, the enemy must fire on average 600/0.30 = 2000 damage worth of ordnance at you in order to kill your ships. 15% of 2000 is 300, which is greater than 165.
Therefore, by removing some shield generation and adding stealth armor, you will increase your ship's survival time. (Suicide Junkie)
2.5.2.1.2 Scattering armor
2.5.2.1.2.1 The situation with scattering armor is very similar to that of Stealth armor. The difference is that the scattering armor is less efficient. If given the choice of ONLY Stealth or Scattering armor, go for the stealth armor first.
2.5.2.1.2.2 At max tech, the value of scattering armor can be calculated similarly to that of stealth armor.
The only difference in this case is that you should use 290 in place of 165.
Using the example given for stealth armor, you can see that scattering armor would only barely be worthwhile. (Suicide Junkie)
===============================================

What does this mean?

I thought stealth and scattering armor gave the ship a 15% defensive bonus, thus making it harder to hit. And once hit, a ships damage is calculated normally.

Where did 165 and 290 damage points come from? And what is the explanation for their use?