If the AP
makes it impossible to roll the result on a D6
then it ignores armor.
Technically incorrect. You have an armour save, it's just an armour save you might not be able to make on a D6
. Positive modifiers might cancel out negative ones.
Example: You have a 5+ save, and are hit with an AP
-2 weapon. Normally you'd need to roll a 5+ on a D6
-2, which would normally give a result range of 1-4 (since anything less than 1 counts as 1), which means you can't possibly pass the save.
However if you were in cover, giving you a +1, you'd have to pass a 5+ on a D6
-2+1, which gives a result range of 1-5, so it's possible to pass.
There is an important lesson here that even the best of us forget, the modifiers alter the DICE ROLL, not the characteristic. A model with a 5+ armour save that is hit with a AP
-1 weapon still has to make a 5+ save, not a 6+ save, it's the dice that is changed from a D6
to a D6