With Nikon 9000 & 35mm slides, SF8 in batch mode does a pre scan. Then as you can see in the scan progress box, lower left corner, it will say Auto Focusing. Somewhere there is a way to Show Auto Focus Point. Looked at this a long time ago but seemed to just key on a very high contrast edge that may be far from the center.
If batch scanning I just go with auto focus. If some film is very dark I do a manual pre scan and set the focus point. It can try several times to find where to focus and that can take longer than doing it manually. May be at times it just can't find a place and then defaults to where the center "usually" is. Just guessing here.
