[ChrisD (Chris)]

I've been using Hocus Focus for a while now, maybe I can help.
If you've setup the focuser step size in Aberration Inspector you should be getting the backfocus error in microns. However, this value really isn't helpful as how far you need to physically increase or decrease the backfocus is dependant on the telescope and flattener optics.

Looking at the corner stars does, in fact, tell you how you need to change the backfocus. See image below. Can you post an image of what you're seeing?

What I do is use the take an in focus image and using the diagram to determine if I need to move in or out. Adjust and recheck. When backfocus is close then use Hocus Focus to fine tune.

I use the hyperbolic curve graph in Hocus Focus to adjust backfocus. Use the centre focus point as reference. When you have all 4 corner focus points around the centre focus backfocus is good. If the 4 corner focus points are grouped left or right of the centre focus point you need to adjust.

For tilt, the further the corner focus points are spread out, the more tilt you have.

If the corner focus points are tightly grouped and close to the centre focus, backfocus and tilt are ideal.

Just a warning for others, if you're using an SCT the star shapes in the diagram are reversed, move in becomes move out.

Chris.