Limited by amount of XM collected?

Is anyone else finding their actions limited by how much xm they collect? I can't find dense enough areas of xm to allow me to do 4 hacks in 15 minutes. I can do usually 1 or 2 hacks then I have to wait for a portal to replenish the xm around it before I can do anymore.

Is there some trick to collecting xm. I know that in the cbd xm is very dense but unless I want to drive there it's too far out of my way for me on foot.