The SSD modules used in the Late 2010 MacBook Air are the same for the 11-inch and 13-inch models. The only difference is "thickness" of the SSDs, with 64GB and 128GB modules with chips on one side, while the 256GB module has it on both sides.
The 256GB SSD will fit in the 11-inch MacBook Air, but with a little "play" to it, albeit reverse. It will curve a tiny bit, very minor, but it works. As the saying goes, YMMV, or your mileage may vary.
(I was successful in getting mine upgraded from 64GB to 256GB before I read the thread elsewhere in these forums about the 256GB "not" being compatible. Which is both true and not true. I have not had any issues so far and everything is working great. Other "proof" is that OWC sells the larger capacity SSD upgrades as being compatible with both the 11-inch and 13-inch models and those SSDs are double-sided chips).