Oddball Kra'vak armour vs. railgun notion

I had an idea for Kra'vak armour, and some of you may like it.	It's 
inspired by a very different game system.

Actually, I haven't been online for a couple of days; someone may 
have already posted this one.

Example:
An interclan Kra'vak ship battle is occuring.  A small Kra'vak 
destroyer fires 6 class 1 railguns at a large, Kra'vak dreadnought
with level 2 armour.

The attacker rolls 6 dice, and 3 hit, each hit possibly causing a 
point of damage.  But the armour is level 2.  For each point of 
damage, the defender picks up 2 dice and rolls; each 4, 5 or 6 
eliminates a point of damage.
In this example, 6 dice roll and 3 damage are blocked (on an average 
roll).

Number crunching here may indicate the threshold for defender's 
success should be changed.

Advantages:
Smallest railguns can eventually pound through any level of armour, 
yet expect very little effect vs. high armour.
Predictable degree of defence from armour (level-1 stops half of all 
damage as written, level-2 stops more than 3/4 of all damage as 
written).

Disadvantages:
Requires defender to actively roll to prevent damage.

Possible tweaks:
- higher threshold; ie. require 5 or 6 to stop a point of damage
- level 2 armour doesn't get 2 dice, just better threshold
- roll against each hit, not against points of damage (significant 
vs. level 3 railguns)
- 6's in defence might stop 2 points of damage to better mirror 
attacks