The problem lies also in the RPMs below max power. Because the shape of the fixed pitch prop is designed for a specific range of speeds, the prop rapidly loses efficiency below certain settings. Idle RPM is around 700 but youre not developing any power to speak of, so your 0% power point is somewhere there. This is different again when flying. Your prop may be developing more drag than thrust at settings around 1300-1400 and below. So where is the 0% power point?? Certainly not at 0 RPM!
As you can see from the figures posted earlier, there's a small band of RPM figures at the top end of the scale where you can go from almost 0% to almost 100% RPM. This band is not linear and it also shifts depending on altitude, speed etc.