Umm, it sounds to me like your assuming that his slave windows are buried behind his main window. Funnily enough he actually mentions moving his mouse from one window to another. You need to pay more attention
Fyi...even if you have all of the windows tiled (i.e., no one window "covering" any other windows) there can only be one in the foreground at any given time. Thus, the remaining windows use the fpsmaxbk setting.