I seriously doubt you get any better focus with a “U” shaped curve than a “V” shaped curve, and will probably get worse results. You are under the impression that having only one low point and “hoping it’s on perfect focus” is a bad thing. Actually the Quadratic and Hyperbolic fit routines are more sensitive to the data points on the wings than they are to flat data points in the low area. Think of it this way: what if all the data points are near the low point? You will get terrible focus results. You really want a nice “V” for best results. Where the one low point in a nice “V” curve is has very little effect on the central point determined by a Quadratic or Hyperbolic Fit. The wings are determining this, and the stronger they are, the better.