I've been wondering about this since my last game. The rules say to round down in the defender's favor, but they don't mention what to do if you have less than 1-2 odds.
In my last game, I used a 1 power infantry to attack a 4 defense main battery. I used the 1-2 odds table since it is the lowest. Was that correct? Or should you just say that an attack has zero chance of winning unless it has 1-2 odds?