"1/8, semi bank"? I always wonder what that means! I like to do spreadsheet calculations and I have a couple of spreadsheet set up for calculating, not only rear stagger, but how that's affected by banking. I wonder; is the track mostly flat on the inside of the turns? Is the racing line arc close to the inside edge of the track at the apex?
Have you ever measured the distance between the straightaways? 1/8 mile track covers a lot of different configurations. Tight turns, long straights, wide turns, short straights.
I have no experience with dirt ovals, only paved, so my advice may not be of any use, but I'd like to think it is.
How wide would you say it is, measuring at about the center of the straightaways, from one inside tire path, across the infield, to the other inside tire path? You could walk it off and count each step as about 3 feet.
I have this idea that stagger can be calculated based on that measurement. For instance; if that measurement ended up being 80 feet, the calculated stagger would be 2 1/4". I have this theory that stagger should be based on the radius of the turn. I have this theory that if you change your stagger, in an attempt to cure some handling problem, and you go faster, it's because you are now closer to the correct stagger, rather than anything else.
With no further information, just speculating, when you went to 2 inch stagger you got closer to the right stagger, not because of anything else. Of course change in your stagger that much had to affect your corner weights. Corner weights can definitely change handling!