Speed from new iPad/iPhone 5 and distance variation

I set up a new airport extreme today. I'm connected wired via my computers and wirelessly for the ipad 3/iphone 5. I'm having issues with the wireless speed. I'm using the speedtest.net app for the testing. When I'm 10 ft away, I'm getting a good 20Mbps dl (my internet connection is only around that so it is the limiting factor). When I move to 20ft away, I go down to 2-5Mbps on both the iphone and ipad. I thought the range should be a lot longer. Note that I am getting full bars all the time and the upload speed seems fine. It's the download speed that decreases drastically over this short distance. Am I doing something wrong or should I configure the airport extreme differently?