The rule for determining how many focuser steps you should have between data points is that the biggest HFR reading you get should be about 3x the smallest HFR. So, if you are seeing an HFR of 1.2 with good focus, adjust your steps between data points so that the first data point that is calculated has an HFR around 3.6 - 4.0.
Also, HFR is not an absolute – it’s totally dependent on your equipment. Some systems get perfect focus when the HFR is 3.5 and other get it at 0.5. HFR is in pixels, BTW, not arc seconds.
Also, the V curve will only be symmetrical when the camera was already in perfect focus when the AF routine started. The more asymmetry you see, the more the camera was out of focus to start.