The exact tightness of the for-end is not an exacting science. But I agree, if a for-end is so tite that it inhibits the barrel from dropping open when the release is depressed, it is too tight.
Tim gave a good analogy, when open, the for-end, merely keeps the barrel from falling off. Just tite enough so as it doesn't fall off the barrel with out the screw when closed.
CW