Hi Buzz,
I don't thing collimation is a problem here. Stars are seemingly round across the image. I'm sure my collimation isn't perfect, but I think it is collimated well enough to not cause problems with the AF routine. If the hot column is a problem during a night, SGP has no troubles getting it's v-curve and in situations where it doesn't get the v-curve, the final focus position is usually calculated right on the mark.
My step size is 75 and my FL is 1624mm with 1x1 pixel scale of .69 arcseconds. So if the AF routine is thrown off by slight variations in the frame, generally the CFZ size is large enough to accommodate where it my land.