Strngr - I have a feeling that unless she's dictating when you get to see your child, it's going to be "unfair" - you said before she has a bit of a princess complex, right?
You could invite her to help come up with a schedule. Send her what you have and ask for input. I wouldn't expect anything rational, but making her part of the process might make her more agreeable.
You, stick to your guns. There's really no way to make anything to do with children completely fair. Since there are 7 days in a week - a 2 week spread is the way to go. I've just read enough of your thread to have reached a conclusion that unless it's her calling the shots, she seems to get upset about something.
Just be as pleasant and non-confrontational as you can be. You have a right to your son, and are not trying to be unfair. You're trying to work out a schedule both of you can live with. Asking her input might bring the tension level down a bit, though.