Following will make rendered svg smaller by device pixel ratio (ie. at 2x will become half size):

Image {
  source: "file.svg"
  sourceSize: Qt.size(width,height)
}

Looks like it is evaluated before the final size is known, which is expected, so it sets it 0x0 initially. But after the image is loaded, the size reported by width and height properties seems to be half the expected size at 2x scale ratio.