The only reason it could be moving around is based on two things.
1, size of art.
2, you may not be using this process.
When in illustrator:
Use Save As, EPS. Use artboards (document size)
And the range. The range is nothing more than ...is it page 1, 2 3 etc. there is an artboard window. You can set a left chest up as one file, (range 1), save and print....designating the range (what page you want to print).
then, you can print the other one. Full back. Artboard or "range" 2.