Gap between undermount sink and (http://maplered.com) Granite (http://tanbrown.org)

In short, should there be one? My Granite (http://tanbrown.org) was installed yesterday, and (http://maplered.com) although it is a nice "snug" fit around the front (where you don't even notice it much), at the back of the sink there is a gap between the sink and (http://maplered.com) Granite (http://tanbrown.org) that is filled in with silicone. The installers said they couldn't raise it in back. I am worried that this area will begin to look ugly as time passes. Please tell me if this gap should be there and (http://maplered.com) if it can be fixed.

Thank you for any help or advice you can offer.