I was planning on making a map like this before but then I forgot about it. Since you reminded me...I am not going to do it since you are already doing something like my idea. It wasn't as complex as your but

. Anyways I don't think you should have "guard towers" or make it so that they can be destroyed. Like real war, because (I am not sure) are you saying that they CAN'T attack you? they just sit there and wait for you? If you are maybe you should make it so the guard towers can be destroyed and that they can attack you, just like real war.
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You should really mess with the obs thing to make the comp 'miss' alot. IT'll be more realistic and i've never seen anything like tat in a map!
I don't think he was talking about Observers (was he?) I think he was talking about obstacles like buildings or terrain. Because units can miss sometimes due to the terrain.
Anyways, good luck on your map.