Really? I'm surprised this works. I've actually had more luck with mid-back seats (rows around 15-17 are best). I find there are three kinds of middle-seat takers:

1) Grab the first one they can find, generally up front.
2) Walk all the way to the back to see if there are any available aisle/windows. Once they have scouted the whole plane, they might as well grab a center in one of the last rows because there are now people in the aisle in front of them.
3) Find an "attractive" set of occupied aisle/window seats. This might be literally an attractive person, a small person (e.g., a 5-year-old), or a unite-the-couple possibility.

I figure 15-17 is still the best odds, to avoid types 1 and 2. When I fly solo, I always look for the worst possible seatmate in a row by themselves (preferably a COS in the aisle) and grab that row, especially if it's mid-back, to avoid type 3s. However, I'm out of luck when I bring my own 5-year-old (small) row-mate with me.