Hi Hamish,
in parallel projection there is no such a thing as distant or near object, so if you zoom (go closer to object), your object is projected same way as before.
But in RC there is a way to “zoom” view in parallel projection. Just hold SHIFT and use mouse wheel. In perspective projection you change this way focal length of camera. In parallel projection is focal point in infinity and what you change this way is rather scale of scene than focal length.