I'd be interested in seeing your actual report definition. The widgets you're using would help to answer your question accurately.
I think, though, from your description of the problem, you are using the Device Type Summary widget. That widget counts the number of sessions by device type rather than the unique clients. So you would not only show the client once for each controller, but once for each time it connected to any device.
Although it looks to me like you might also be using the Devices widget, in which case I'm less clear on what your seeing.
As I said,, it would help to know what your report definition actually looks like.