When you press the left button, this hotkey will click the same spot in both windows at the same time, even if the windows are different sizes.
But there's a problem. The hotkey will get triggered every time you press the left button. Most of the time you want the left button to work normally. You need some way to control this behavior so it only happens when you want it to.
One way to accomplish this is by rewriting the hotkey so it only happens if you hold down a certain key at the same time as you press the button.. Suppose you decide to use the Oem3 key for this purpose. (That's the key in the upper left corner of the keyboard.) You need to define that key as a custom modifier and then include it as part of the hotkey trigger.