Problems with post backgrounds

Hi,

I have a site that I have used some old paper as the post/page background. but what happens is that when there is very little on the page the background shrinks. I'm not sure whether it is better to keep it one size which I haven't figure out.

Another way would be to make the container background transparent. For some reason transparent just doesn't seem to work. (Seem to have the same problem with the header which I posted in another area)

I've looked for a post but have not been able to find one yet.

I'm using ATA 3.7.9 and WP 3.4

Thanks