Bomber Efficiency

For bombing a stack that has a mix of unarmored and armored, is it better to have a 10 stack of just Tac Bombers and a different stack of Attack Bombers, or should I combine them proportionate to the ratio of the stack I'm attacking? Ex. 6 Unarmored, 4 Armored, Should I have 10 of each in different stacks, or 2 stacks of 6 Tactical and 4 Attack Bombers?