Okay, here's the deal: I believe that time is the predominant factor in dry hopping, and I had previously thought quantity was just as important.
I did an IPA with Rye, double dry hopping, divided into:
- 1.5 ounces of hops for 4 days, 1.5 ounces of hops for 4 days
- 3 ounces of hops for 4 days.
Though I did not expect a difference, and with the help of a friend who is very good at distinguishing differences, we determined the first batch was significantly more aromatic. This is somewhat noticeable in the smell, but also very pronounced in your sinuses, a great addition to a beer I'm now quite proud of.
This seems to validate that a significant amount of your aroma comes from time in contact with hops, more so than quantity of the hops. Therefore, I would guess multiple additions is the best way to get the most aroma, once you're worried about leaving the hops in longer than x days (many people differ on how long it takes to get unpleasant taste from too much time in contact with hops).