SGII: Non-penetrating hit

Let's say I get a major hit from a missile launcher on a tracked vehicle
with armour 
level 4.

The impact (D12x2) fails to penetrate the armour (D12x4), but the
suspension is hit.  
What is the impact vs. armour test ?

a) D12x2 vs. D10
b) D12x2 vs. D10x4
c) D12 vs. D10

??

Last night's match up had heavy weapons really punishing vehicles
strictly by 
immobilising them and causing the crew to panic and bail out.  Oddly,
enough the crew of 
one tank got in position, in cover, and suppressed some overconfident
power armour 
troops advancing  toward the wrecked tank.  They were one of the only
pleasant surprises 
for the defenders.

Tom