Can you put the cover before the contents?

Rashi explain that the Torah devoted an extra pasuk to teach us that we first put the Luchos into the aron and then the Kappores on top, and not put the Kappores first. I suppose that means that we should not first put the Kappores, then tilt it off somehow and then put in the Luchos. Obviously once the Kappores was sitting squarely on top of the Aron no Luchos could possibly be put in. So the question is why should I have thought that we should specifically first put the Kappores on? The kinderlach suggested that the Aron and Kappores were really one unit, a container and its cover, and the Aron was simply incomplete, and thus of no legal bearing, unless it had its cover with it. So would I have thought. The extra pasuk teaches me that this is not so.