Update : I managed to get this keyword at #5 now after 2 months, aiming for #1 now...
Who's advice did you follow in the meantime?
Now that you're almost on the first page, G is testing the user experience that your site delivers.
They have you parked at 11 to give you a little bit of traffic, and see;
a) how enticing your site is to people who see it in the SERPs (your CTR)
b) how quickly that traffic bounces from your site
If you have a good CTR and a low bounce rate, your rankings will improve from number 11 without you building a single link more.