I have been using SGP for focussing for some time now and have had no issue with it. I recall that there used to be sliders for star count and nebulosity (or something like that). There is a new system that involves setting a minimum star size at 1x1 pixels. I have never had to adjust this from its default of 6 - it has just worked.
Last night, however, I was imaging M33 in Ha. I noticed that the focus routine was picking up some of the Ha in the galaxy - NGC 604, in fact. So I had to look at the manual. I tried various settings for min star size - up to 8 and down to 2. I was never able to exclude NGC 604. As it turned out, even though the reported HFR was around 1.6, I think I got good focus anyway. I slewed off to B-Andromeda and checked with a Bahtinov. But I would prefer to be focussing just on stars if I can.
I will link to a screenshot showing what was happening - https://dl.dropboxusercontent.com/u/54557410/Focus.jpg
Thanks in anticipation