it would be nice to know when certain reinforcments options occur.]

1) Sometimes you go onto the battlefield and you are controlling your army and the AI is controlling your other army in the area (of course have no way of deciding which one you'd like to control).

2) Sometimes the reinforcments wait on the edge of the battlemap and they become ready and come onto the field automatically once there is room in your stack (I don't really know how this one works, but it's the one I like the most)