The other thing that your spreadsheet would need to know is the radius of the actual object you're crashing into. I suspect the exclusion zone is some formula roughly like (object radius + X distance), where X depends mostly on the type of object in question - whether it's a terrestrial planet, gas giant, normal star or giant star. It would have to be additive to the object radius, otherwise you might get some weird edge objects where the exclusion zone is calculated to be inside the star or planet.
White dwarfs would seem to count as "normal" stars, which is why they've got his huge exclusion zone around them; it's using the same formula (and same thickness of exclusion zone) that it uses for full-sized stars.