Ah, I think I understand your question a bit better now. Using the same seed no on a different size map will result in a map that will look pretty similar from a bird's eye perspective, but very different in detail.
Did you think that, after having drawn a nice start spot on a medium map, you could recreate that same starting spot on a huge map? I think that would not quite work; starting spots, rivers, resources and everything would move about too much. I'm not even sure whether strategic resources would still be roughtly located in the same positions. And 16 starting spots instead of 8 will mean a big reshuffle, as you can imagine.
I hope this is a bit clearer.