Don't compare SS drop measurements with non SS cars..the SS is already lowered from the factory so you wil not see the same amount of drop(total) with the same springs...the final ht will be the same minus the difference between the tire diameters but thats it...
EX: An LT may see 2.50 drop in the rear while a SS wil only see 1"..so in the end both cars wil sit the same...minus tire ht..