I can't get the device screen size in real pixels

Hi ! basically I've this:

console.log(DPUnitsToPixels(Titanium.Platform.displayCaps.platformHeight)));
function DPUnitsToPixels(TheDPUnits){
    if ( Titanium.Platform.displayCaps.dpi > 160 )
          return (TheDPUnits * (Titanium.Platform.displayCaps.dpi / 160));
    else 
        return TheDPUnits;
}

According to Apple, i6p had 1920px of height while ipad air: 2048

What's wrong with the function ?