How large is the image you are using? i forgot to mention that sorry, try making the circle size to range + image radius.
Example 250px range, image diameter 100, circle size will be 250+100/2 or 300. If this does not work try tweaking the number until its right, also you should note that if the size of the towers are different this will need tweaking even more, using as close to circular towers will work best. This is because the range 250px starts soon as the image ends, but the circle we are drawing starts from the center of the image so the range looks bigger then the circle itself.