Like you said, shoot what the rifle likes, doesn't matter how you arrive at the preferred seating depth.
Establish a starting point, be it just on the lands, just off the lands or even jammed hard into the lands, it doesn't matter, that 8 thou figure you state doesn't mean a thing, it just provides a place to start that is as good as any. Find the best powder weight at that seating and then tune the seating and finally fine tune the powder with the new seating.
The more neck tension the more you can jam the bullet in the lands without it moving, this will also be effected by the shape of the bullet. I load Ultra's at 20 thou past where they first just tough the lands, the marks are much longer than they are wide. People say that the bulley must move jammed that far, they do not. On the flip side a low number ogive like a 68 grain Berger for example probably will never jam that far, the bullet bangs the lands and cannot be jammed into the lands very much, the result of the blunter shape with less taper to be able to wedge in.
I'd pick a bush that gives you about 2 thou tension, tune for that and then try a bush size either side. Alter one thing at a time.
