pinion depth, how close does it have to be

Setting up some new 8.75 489 gears, it seems like 2 thousandth of pinion depth is the difference between too deep and too shallow. What's the typical range? Setting up used gears wasn't this fussy.

I had the pattern perfect but noticed the lash had closed up a thou. Dammit. Setting it back to 8 thou threw the pattern off again.

Does anybody enjoy this job lol