Either what they said...or the opposite. Most A cat guides explain it like this. If you can point well but the boat tends to not squirt in a puff, you need to flatten your sail. In order to not go over in a puff you have to point very high...your speed goes down, and you are pointing higher than your competition.
If, on the other hand, you have speed in the puffs (squirt) but can not point as high as the competition (especially in the lulls), then you need a fuller sail (more power).
Since you said you can not trapeze until the wind is up around 15 knots and you can not point, I think you need more power. With your boat you should be on the wire around 6. There are people that stop sailing at 15 knots and you are just now able to go out on the wire? Or do you just not go out before 15 knots?
The trick of lying the boat on it's side is to help you tune the mast. If, for example, you decide you want to have a flatter sail there are two ways to achieve this. You can crank on the diamond wire, or rake your spreaders back (or some of each). When you crank the diamonds you will get more bend up top and less down low. When you move the spreaders back you will get more bending down low. This technique helps tell where to adjust for your sail, not how much bend your sail needs.
Also, the square top is more sensitive to main sheet tension. Make sure you are in tight, especially above 5.