No, you can't have a window with a different pixel size on one screen and another. Trying to emulate this using two windows would not achieve a smooth experience.
OTOH it is questionable if this is really all that important. Most of the time if a window spans more than one screen it's temporary because you are just moving the window from one screen to another.
OTOH it is questionable if this is really all that important. Most of the time if a window spans more than one screen it's temporary because you are just moving the window from one screen to another.