The left side of chris' curve is really low. There's about 6000 points from full open to full closed but there's only about 1000 useable places that can be selected. The points in between are used by the compensation when the curve gets scaled according to the ideal gas law. If that low dip goes down to about 5% of 1000 that's a solenoid output of 50 of 1000. A change of 1 step results in that 50 becoming 49 which is a change of 2%. That's a huge change. If he closes the LSN he can move the curve up. Say he makes it so the curve low point is now around 25% of range. That's 250 of 1000. A change from 250 to 249 is 0.4%. you can see that raising the curve that way increases the resolution between values so you can get better control over the mixture.