I would go the other way around:
jQuery(function($) { // DOM READY AND SECURE $ ALIAS
var winIsSmall;
function testWinSize(){
winIsSmall= $(window).width() < 768; // BOOLEAN
}
$(window).on("load resize", testWinSize);
$('#ipsThemeViewerScreen').hover(function () {
if(winIsSmall){
// need something here?
}else{
$('.cover').stop().fadeToggle('fast');
}
});
});