Adjusting Bullet Power

I've been playing with adjusting bullet power the last couple of days. It seemed to be a good idea in theory, but the idea of using 0.15 power and adjusting it would make it seem like you could successfully adjust in a small range of power like 0.1 - 0.2. In practice, if I didn't make an error some where, this is far from the case. I'm seeing a range of more like 0.1 to 1.5, and anything over about 0.4 is, in my opinion, way too high a power for a shielding shot. You might be able to improve slightly keeping a small range of power like 0.1 to 0.2, but it will often be far from hitting the midpoint.