When I do crunches/sit-ups, I feel like only the top of my abdomen is getting a workout.?

When I do crunches, I don’t feel the “burn” in my lower abdomen, like the area around your belly button. That’s where I need it! Here is a picture of where I feel “the burn”:

http://img144.imageshack.us/img144/1527/torsowebzk7.jpg

And here is a picture of where I want to get a workout:

http://img251.imageshack.us/img251/3830/torsoweb2sn1.jpg

I do just regular crunches and I squeeze as hard as I can when I do them.
Thanks!