Help with exit loops/offbeat (on a XDJ)

Hi guys!

I have a question about loops which are set on a XDJ-700.

I'm a simple dj and most of the time i set a loop during a mix or to expand the mix.
But sometimes i like to play more, set a loop and shorten it to create a nice buildup.

But... and this is the question itself: How can i shorten a loop [ like 1/8 1/16 ] during a mix and exit it WITHOUT being OFFBEAT with the other track?