I had to add my 2 cents when you mentioned the "sweet spot". I agree with several of the good answers in this thread, but just to add, instead of needing 2, 3, or more fills to get to your "sweet spot", think of it as if each time you get a fill, you are RETURNING to your "sweet spot". As your body changes (shrinks actually) you need fills to keep getting you back to your sweet spot - the spot at which you eat X amount of food and feel satiated, but it's not enough food to keep your current weight, so as you continue to lose weight and your size changes, the fills just bring you back to the sweet spot again where you feel satiated but you continue to loose weight. Another way to look at it is like your one true "sweet spot" is years down the pike when you are at the point at which you eat, feel satisfied, and MAINTAIN your newly achieved healthy weight.
Good Luck!