Setting up a 5.1 Polk system. I have fxi3 on the way for my surrounds. I dont know if I am going to use them as dipole or bipole so I dont know if they will be on the sides or back. I think they can mount on wall but since I may move them around to experiment I think I want to order some speaker stands for them. How high should these speakers be placed? The stands come in all different sizes.