This isn't magic or hidden science and doesn't require a PhD to understand.

Manufacturers now make inserts specific for their shafts. It's not like the old days where the insert could be wiggled around in the shaft and you had to make sure it was square while the glue set.

If you square the end of the insert more than likely the tip/broadhead will be square with the shaft. If not then the tip/broadhead is bent. Tolerances have been greatly decreased and inserts come sized for the specific shaft. Carbon manufactures usually have the ID the same for a line of shafts and therefore only have to have 1 insert. Aluminum manufactures make inserts that have to be gently forced into the shaft.

If you buy the inserts from the manufacturer there is nothing to consider. I really don't know how we shot arrows all those years without having the tolerances that are used today.