My question is in the tilte. For example, as the CSA, if I have a stationary stack in a region B and a US stack moves (by train or not) from A to C passing by B. Will the US stack engage my stack?
Indeed, though I'm taking "passing by" to mean moving through region B (which on second thought doesn't seem quite right). If they aren't in the same region at any point, there is no chance of battle occurring.