2013 Airport extreme and retina macbook pro issue

[bustyshrimp]

Hello everyone! I recently purchased a late 2013 retina macbook pro and and airport extreme. I am having a random issue when sometimes my rmbp would be on 802.11n instead of 802.11ac. This is even when I sit next to my router on my desk. I have seen my rmbp on 802.11ac in the same spot in my house before. I was wondering why my notebook switches to 802.11n. Also when it switches it stays on 802.11n without ever changing back to 802.11ac. The only way for me to change it back to 802.11 ac is to turn the wifi on and off again. Can someone please explain to me why this happens or if it is supposed to happen? Thanks.