My hood was "collapsed" in the middle. It seemed that someone had stood on it or put a lot of weight in the center, and it caused the gap to be unadjustable in the rear like you describe. Funny, it wasn't creased, or bent, just sprung so that it didn't close right.
What I did, since the hood was in excellent shape otherwise, was to use a wedge under the back of the hood and the cowl, and close it, leaving it for a couple of days to form the hood back to its original shape at the rear. It has worked fine since.
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