I agree with EDude.
If you're not bringing enough pvc for the entire length, I would go UNDER the last rib, then fold the extra fabric forward and secure it.
The reason for a tight fit is that flapping=failure.
This was hammered into me by Bob, Elliot, Dr. Placibo, and others during my intro thread.
You must have found better shark clamps than I did, because if I don't fold fabric over a 1/4 inch piece of cord and place it at the back of the clamp, the clothe ALWAYS slips out.
Oh, by the way, It's beutiful, beutiful.