I think I'm on the right track now - I've uploaded a small project to illustrate - https://www.dropbox.com/s/2o627yfl6ca494n/star%20field.aep.zip

If you turn off the size layer map you'll see how much it's affecting the size. Of course I've got that horrible band in the middle but I think with a couple of form layers and some "horizon" stars I should be able to get it to work. 

What do you think?