Thank you John, Nou.

I took into account your remarks, and I believe I reached a non-textbook-orthodox-solution, at very least, it seems persistant through various autofocus procedures with different filters. Nevertheless, I'll continue studing it since this is much deeper as I thought, considering John's remarks.

I measured microns/tick and it is 0,7636 microns/tick. My resolution is 0,96 arcsec/pixel with a 203/800 Newtonian using ASI1600MM (sensor with pixels of 3,8microns and 4656x3520) I believe I also introduced wavelengths by filter (roughly)

I'm sorry but I skept what advisor propose me: 18 ticks with x5 multiplier. I went to 75 ticks initial step with No OverScan and no multiplier because I changed the algorithm to use to Polynomial and increased tolerance to 10% (instead of 5%, I tested with 20% and 10%, I can imagine the lower the better focused image) Seeing and temperature difference of the primary and ambient is something that should be seriously considered. I could say before that it was important, now I believe is critical!

You can see all parameters below. Like I said, solution is not orthodox (I ignored advisor) but it seems to work so far.

I'll keep testing and improving my knowledge!
BTW: Among the screenshots there is the solution autofocus found for L, Ha, Oiii & Sii. Next step I'll try the "Offset Generator" to put more time on imaging and less on focusing.