Anne,
I like how you articulated that there is not necessarily one correct ratio. The proper ratio can and should depend on each individual course. I agree with the examples that you give that the content can and will definitely play a role in the proper course ratio. Other factors such as the level of the content, the design of the course (interaction, discussion, etc.) and other factors also influence the ideal ratio. I have personally found similar ratios in my experience teaching online.
Herbert Brown III
