Wild wing how do you get it so precise?
It's like when the kid asked the old man how do I get to Carnegie Hall?
The old man said, practice son, practice...
I've been doing it for 40 years, so that's part of the answer. But here are the steps:
After installing the tip, wrap the ferrule with tape. I recommend Scotch freezer tape, as it comes off the easiest without leaving a residue.
I put the shaft in a thick towel, and put gently in a vise, so I can use strips of sandpaper and rotate the shaft inside the towel. I use 400 grit sandpaper for this. The sandpaper contacts the tip and tape, but not the ferrule. Don't sand too much on one piece of tape; keep replacing the tape after a few rotations, or you'll sand through the tape.
After several pieces of tape, you'll get to the point where it's hard to sand down any more tip, but you'll still have a little lip of the tip beyond the ferrule. At this point, you put the tape on as usual, but 2 to 3 millimeters or so below the tip, exposing a tiny bit of ferrule. Don't worry, the thickness of the tape will prevent you hitting the ferrule. Keep sanding with the strip of sandpaper, but check the tip carefully after each rotation until you've got that tip nice and flush, but still no contact to the ferrule, as you can see. Once it's perfect, finish the sides of the tip by burnishing, and shape the top of the tip.
It is a bit tedious to do, but you asked how I get it precise. Those are the steps.
All the best,
WW