@mixin background-image-dpr2($path, $file, $width, $height, $params:"") {
  @if $params != "" {
    background: url($path + '/' + $file) $params;
  } @else {
    background: url($path + '/' + $file);
  }

  @media (min-device-pixel-ratio: 1.1), (min-resolution: 1.1dppx) {
    & {
      background-image: url($path + '/dpr2/' + $file);
      background-size: $width $height;
    }
  }
}

@mixin background-image-dpr2($path, $file, $width, $height, $params:"") {
    @if $params != "" {
        background: url($path + '/' + $file) $params;
    } @else {
        background: url($path + '/' + $file);
    }

    background-size: $width $height;

    @media (min-device-pixel-ratio: 1.1), (min-resolution: 1.1dppx) {
        background-image: url($path + '/dpr2/' + $file);
    }
}

Set background-size at normal device-pixel-ratio
Set background-size at normal device-pixel-ratio

This prevents inconsistencies bewteen normal and hi-res screens when
the sizes of the image and the container do not match.
