Not sure if this was your intention but I can put radar towers around any other tower and they stack. So if I put 8 radar towers around a heat ray tower the range becomes ungodly.
Poorly developed game. Towards the end I was building towers as fast as I could but couldn't keep up. Money is just not an issue in this game it is all about how fast you can build the most towers before you die. Not fun. 1 star.
Great game.. I would also like to see more in depth quests. Also it needs a quit to menu option, and 3 save slots to progress the 3 different characters.