Mortgage interest and married filing separately

If my wife and I file married but separately, should we enter the full amount of mortgage interest in the application and the full tax amount, or should we check the box and indicate half of the mortgage interest on the page leaving the note that we're married filing separately?  We currently pay all home costs from a joint account.

 

If we half the interest on that screen, do we later go by the mortgage cap of 375k or we use the 750k figure to answer the question?