genesis atmosphere pro: change front page backstretch widget image ratio

I’m trying to change the backstretch background image ratio on a home page widget. The default image size used is 1600 x 1050, and I’d like to shrink the height to 1600 x 750.

Does anyone know how to change this? I don’t know js, and I’m not seeing anything relevant in the style sheets.

I was thinking this is setting the image class as .front-page-1:

jQuery(document).ready(function($) {

	$(".front-page-1").backstretch([BackStretchImg.src]);

});

and this is setting the height?

jQuery(function( $ ){

	// Set front page 1 height
	var windowHeight = $( window ).height() - 77;

	$( '.front-page-1' ) .css({'height': windowHeight +'px'});

	$( window ).resize(function(){

		var windowHeight = $( window ).height();

		$( '.front-page-1' ) .css({'height': windowHeight +'px'});

	});

…but I don’t know what to change. If I upload a 1600×750 image, it zooms in and maintains the old ratio.