I have struggled with getting EKOS to autofocus with my Esatto and C11.
I discovered that I needed a much larger initial step size than I had thought, which ended being an initial step size of 30,000! The Esatto has 420,000 steps, so 30K is not has large as it seems. I tested it with the Polynomial method and it achieved perfect focus in just 7 steps. Repeatedly. I was never able to get the Linear method to work, as it still stops at the wrong spot after calculating the correct one. But the Polynomial works great.
So the advice that solved this problem was simply to manually achieve perfect focus, measure the HFR, and then see how many steps it takes to get an HFR values 3 or 4 times higher. With the Esatto, that turned out to be 30,000.
iOptron CEM120 EC2 and CEM25P
Celestron C11 EdgeHD
William Optics Star71
ASI 1600Mm Pro, ASI 462MC
Moonlight motorfocus & Esatto focuser
LodeStar X2 and ZWO OAG