When you say background with a title block, do you mean a title block on a background page? Or is this "background" on the drawing page?
If you put it on a background page, it will remain unchanged as you change the scale of the drawing page.
If you have it on the drawing page, consider putting it on a background page. The drawing page can then reference the background, and as long as you don't change the sheet size, then everything should work as you desire.
HTH
Wapperdude