I would say sighting of open sights uses the same principle as scopes.
Generally you would place your target at 25 yards or less to try to sight it as close to the bulls eye as possible and once that is done move onto 100 yards.
If you are shooting to the right of the bull’s eye adjust the rear sight to the left to correct the problem. The opposite applies for the left side of the bull’s eye.
If you are hitting the target above the bull’s eye then adjust the rear sight lower and if hitting the target below the bull’s eye then adjust the rear sight higher.
My Williams FP rear sight had the instructions included. Maybe yours will have them too.
I took the williams sights off... because in our cowboy local we had to have open sights or tang .. could not have a receiver sight... I had figured out the ups and downs but as far as putting the front globe on..'
I quess you just try and eyeball it center???