Blender Video Editor not zooming/panning correctly?

Hi. I’ve followed some tutorials but BVE doesn’t seem to be zooming out/panning as I expected.

I’ve started a new Blender project, switched to video editor layout and set properties to 1920 x 1080 (60fps). I’ve then imported a large image (7680 x 4320) and ticked “image offset”. So far so good. I’m presented with the bottom corner section of the full-resolution image.

I’m trying to create a scene which starts with a close-up (showing the small section of the image at 100% resolution) and then pans out (showing the entire image at something like 25% scale). So I add a transform strip, set it to over drop, tick “uniform scale” and reduce the scale to less than 1.0 and it pans out but unfortunately it’s cropped out the rest of the image. This is the problem. According to the tutorials I expected the rest of the image to appear but instead I get the black/grey chequerboard. Incidentally, “crop image” isn’t checked. Anybody see where I’m going wrong?