Need calculation help!

I don't know how to answer that except to say that armor and cities do not go together nicely. Try to place non-armor such as anti-tank and anti-air in cities.

Yes, you got the math right.

Think of it this way.

SBDE is a measure of how many of the units in the stack can actually effectively attack/defend. Beyond a certain point, in a stack, more units will not be able to get to the enemy past their own units. This means those extra units are not included in your combat strengths.

The terrain penalty/boost is entirely separate from the SBDE focus. Terrain effects all units of the given type in the stack. So, LTs in a city all have a 50% reduction in strength. More LTs, beyond a certain point just get in the way of the ones that are doing the best they can.

Somewhere around here there is a thread that lists the number of each unit type needed to get 100% SBDE. I would never put more than that amount (+1 for battle losses) in a stack. I think that number for LT is 5 so split that stack up and get it out of the city.

Thanks for the responses - I understand SBDE and terrain analysis.. But - I was attacking this stack not building it - guess I should have clarified.

For your future needs, try this:

Battle Calculator

@DxC has done excellent work with it.