How to set the window size in multi display?

Hi, now I am testing the multi display in unity5.3. I am contolling 2 display in extended mode. primary display : disp0, secondary display : disp1 If I use the disp0 and disp1 in full screen, ok. But if I am going to use disp0 in 1024*768 mode, bad. disp0: 1024*768, disp1: full screen. How to do for this? thanks.