pitch controls angle of main rotor blades. The higher the angle of attack. (angle between blade and the wind coming in) The more lift is produced until a high enough angle is reached where the air cannot stick to the surface of the blade and a stall occurs...
Anyways... when you have higher blade angle there is more surface area hitting the air and therefore slowing the rotor down. In order to over come that more engine power is needed. In regular heli mode for hover and basics. Throttle curve goes from engine idle to full power and blade rpm is tried to be maintained at a constant rate above 1/3 stick. Below 1/3 stick the engine power decreases so you can turn on and shut off the engine safely without cutting yourself.. blade angle ranges from -2 degrees so you can decend at 1/3 stick to 9-10 degrees at full up stick so you can climb. If at full stick the blade rpm drops you need to either raise engine rpm curve at full stick or drop pitch curve in order to maintain rpm.

In idle up mode or aerobatic mode engine rpm is attempted in maintained constant. For example at full up stick you have highest angle so you need more power. At mid stick you have about 5 degrees pitch for hover so you need less power. You need to set that in your curves. at bottom stick you have full negative pitch so you can fly upside down but you have same amount of drag as in full up stick so you need full power also...

Its a bit confusing, tell me if you have any questions.