Mr. Coffee seems to know the future
Your coffee maker puts water into the grounds at the same rate regardless of how much ground coffee you have put into the filter. The water will stay in the filter area for the same amount of time regardless of the amount of coffee in the filter.

If there is less coffee in the water, then there is less of the flavorful soluble coffeeness (various amino acids, caramelized sugars and aromatic oils) for the water to pick up. The same amount of soluble material becomes more dilute in the greater amount of water. Some coffee makers adjust for this and release less water at a time if you are making a smaller amount of coffee.

If the water sits longer in the grounds of will pick up more flavor, but not all of it is going to improve the flavor. If it sits too long in not enough grounds it will become more acidic and more bitter.

Alton Brown has a great episode about the science of coffee, BTW. http://www.foodnetwork.com/shows/good-eats/2-series/true-brew.html