It's normal for the lower pully to be way in front of the upper pulley wheel when you're on big-big. As long as it makes a definite S curve through the pulleys, it's OK. BUT it sure doesn't hurt to make the chain an inch longer - just test it using the small-small combo after you install it and make sure there's no interference. You can always shorten it again, but it's a pain to lengthen it!

Look at this page for illustrations of what I was trying to describe for big-big and small-small. http://www.parktool.com/blog/repair-...-length-sizing