Help with expansion tank location

Hi everyone. Trying to locate best position for expansion tank. Image depicts tank on supply side before close tees with circulator on return side. Four zones depicted with circulators on supply side. I guess the difficulty I'm having is simply that using the close tees am I really pumping away from the expansion tank no matter its location on what I want to call the boiler loop? Image: http://i1189.photobucket.com/albums/z427/BooDaa/Boiler/boilerpiping1.jpg (http://s1189.photobucket.com/user/BooDaa/media/Boiler/boilerpiping1.jpg.html)