Size of the ampules

Has anyone noticed that the ampules have different sizes? I see in an arial shot (View point from the Big Head, "Oscar") that there are a few sizes.. medium, small, and x-small. In the Prometheus teaser traler #3, there is an ampule up to David's chest.. which is pretty large. So that being noted, it would mean that there is a little more than just DNA in the ampules.