not really a big gap if you have a new flaw, a few thin shots can add 5 strokes to your card easy...

As Robert said, its changing your setup "height" that causes these shots.
If you dip you get it fat, if (like me) you stand up you hit them thin.
Its very frustrating because you are 90% towards a perfect shot but you thin it, usually dead straight!
So, moral of the story is make sure you stay down & behind the ball through impact.