Hi in2steam, agree with all you say, hypothetical .001" is achieved by raising the scraper and not paying attention, good for oil pockets.
I scraped on and off as the occasion arose for 40 years.
The first scrape while apprenticed was on M.A.N electric loco main drive axle bearings, about 6" diam shaft 15" long, made from Phosphor bronze.
The old feller on the department was a German fitter of about 80 years vintage, and you didn't call him by his first name, not the appy's anyway, it was always Mr.......
One thing I learned, the hard way, and that was too much blue on the shaft meant a clip round the ear, and fooled no one.
By the way, how many people take their vice jaws off and grind the back side flat and remount with the smooth faces holding the work?
Very few from what I've seen, but it is the only way unless you want to leave deep marks on your work.
When you've scraped three sides it only needs an end stop to stop the job sliding along the bench, like a planer table setup.
Ian.