Ordnance Question for WGC 2013

[Ramzus]

I could not find an answer in the FAQ's anywhere so I thought I'd better ask in advance. When a Medusa fires the Bastion Breacher Shell, it is an ordnance weapon so rolling for armor penetration says you roll two dice and pick the highest. The rules for the Bastion Breacher Shell says it rolls an additional dice for armor penetration. Does this mean you roll three dice and take the highest two? or does it mean you roll two take the highest and then roll another one and add them together?

Thanks!