Focuser step size

[woodsie]

Hi Guys

My riig is as follows

Tak FSQ85 focal length 450 mm Aperture 85mm with standard TAK focuser active draw tube length 497 mm

Focuser Senso 2 resolutiom 0.7 Microns

Camera ASI 183 Mono Pro Pixel size 2.4 microns

From Calculations and Tables I have derived the following

Critical Focus Zone = 72 Microns

One focus step = 11 microns

With the above rig the best auto focus I can get using NINA is between 4 and 6 FHW with a 15 step spacing between curve focus points

Using empirical focuser step calculation methods the step size is indicated to be 35.

I would like to get a better focus than between 4 and 6

Am i over thinking this

Advice welcome