Maximise Image Dual Monitors

Hi,

I use PS on dual monitors, with the tools, menus etc on my left-hand monitor and the image on the right-hand monitor. 

I maximise the image I am editing on RHS monitor, but if I use Cmd 0, or zoom the image the maximised screen will reduce in size and I have to maximise it again.  If I open another image, the screen will reduce in size. 

I have un-checked "Zoom resizes windows" in preferences and it makes no difference.