A 2600 share will count for twice as much as a 1300 share, the only difference would be that it'd increase deviation, but should average out eventually.
That doesn't seem quite right. I just put in a 21,700 share, and it seems to be worth just as much as any other share I've put in.
I put in a 4750 share that got 0.. I don't know if it'll let you set your difficulty to 21700, but if you can and you did, then you would have gotten credit for 21700