Have you remembered to include the Viewport meta tag? The S3's viewport is 360x604, so if you're seeing styles for media queries greater than 360 on your portrait view, chances are you have your viewport misconfigured. I'd encourage the following viewport tag and @viewport
directive (in your CSS):
<meta name="viewport" content="initial-scale=1.0">
@viewport {
zoom: 1;
}
Also take a look at this related question on the viewport meta tag on the S3.