On my Mac the width of the monitor(s) is the ruling factor. Without 2. monitor eg lena,leno dp appear nicely side by side. Size : 1680,1028
With landscape sample its top/bottom!
With the second monitor and large width the position of the second window is difficult, with landscape image as well as lena/o the title line is outside mouse access! With help of the mac window manager it is possible with some difficulties to get the two windows side by side.