Don't terminate the first-pass search if the samples are improving.
Simplify the start-position choice, and don't move quite as far out.
Don't skip samples if the HFR is <= 2.5
Don't use the polynomial min value as the value to search for, rather the min sample so far.

As before, use the simulator, see that it reaches focus starting from 50000, 60000 and 20000 with
Linear set as the focus algorithm, and step size 1500 and full field