The most open to sunlight (and out of the way) areas in my yard for wood racks are along fences. One is a 4' chain link which has plenty of air flow. I'm putting 4 cords near it, stacked in 2 long rows. The other fence is a stockade (wood picket) fence, 6' tall. I know the stockade won't flow air like the chain link. One side should get plenty of breeze, but the fence side will be blocked, obviously by the fence.
Ideally, how far from the stockade fence should I make my stack for proper air flow?
If you are drying wood for this winter, I'd try and leave 1.5 to 2 foot?, but I really don't know what you have to work with or and statistics on how far would make a difference, and would try to leave a gap between each as well.
If it this wood for the future, winter 16-17, then I would be less concerned, and just consider if there is a problem with a leaner stack interacting with a fence.
In all, at only 2 deep, you should still have quite a bit of airflow. Just make sure the footing is sound and you stack well. Also, it's going to depend on the general airflow in the area, the sun you get, how your soil drains, etc, etc. A good part of it is going to be through experience, simply learning what you can "get away with".
With clearances / airflow, more is better, but it's going to take a few years of trial and error for your particular setup and weather to see what you can do.
Planning on top covering both piles? Not at all? Covering together? Also, depends on the wood you are putting up as some dry quicker than others.
There are a ton of variables. If you have the room, getting a few years ahead on your wood helps equalize the variables and make any one less of a concern, with having greater time on your side.