Weird result with camera scaling?

I'm designing this game based on a 800x600 resolution screen and this is what it looks like:

When I select a different resolution, this is the result:

I don't want to have that empty space, so I changed the width of my Camera Viewport Rect with this code:

 float idealAspect = 800f / 600f;
 float aspect = (idealAspect / ((float)Screen.width / Screen.height));
 Camera.main.rect = new Rect (0, 0, aspect, 1);

It works fine when running the game inside Unity, but when I run directly on my phone (Moto G 2nd gen.), this is the result:

Any idea what is causing this?

Thanks.