Background vs. Minimized issues

I am currently playing 2 accounts with one computer, and am looking to add more accounts. I have one wow foreground and the other either background or minimized.

The foreground wow is using ~40% of CPU resources. If the other wow is background but not minimized, it also uses another ~40% of CPU resources. In this case the performance is great. These resource numbers seem to be independent of the priority level, I have tried all reasonable settings.

If the background wow is minimized, it now only uses about ~4% of CPU resources, and again this value does not depend on priorities. The problem is, the background character gets laggy and choppy, for example it starts to fall behind when following. I have even tried realtime priority on the minimized wow.

I would like to have the background resources use say 15% of system resources and perform well so that I can add more accounts without suffering degradation, but I don't seem to be able to make that happen for any settings. Moreover, I do not know why this is happening and cannot find any reference to this effect anywhere. Does anyone have any suggestions?