I don’t know at all if it’s possible but i’m giving the suggestion:
It would be for the jzintv runner to add options to make the window bigger and stretching the game. The runner runs using the native resolution of the games which is very tiny. Impossible to resize the window and the fullscreen just fills the screen with the still tiny game screen at the center.
So it would be nice to add a real fullscren feature that stretches the game, and also adding size multipliers for the windowed versions (2x, 3x, etc… at least until 5x )