Hi Elizabeth,
I wish I could give you an answer to distance, but unfortunately I don't know. I do know that in general, you are going to get seedling variation with new ones you purchased even without cross pollination. Some of the seedlings will look very similar and some will be very different. It all depends on the background of the new plants you purchased on how much variation you are going to see in general. It is fun even if they do not look the same. I grow a blue Siberian and many of the babies are a similar blue. But I now have one that is a beautiful pale blue. So I like it all the more.
Remy