just after posting i remembered a really good example of this. Due to manifold constraints and packaging i went from a VM22 on a moped build to a VM18. Despite being similar design and layout, these two carbs are (obviously) different castings and always end up running really different tuning parts.
I had a 165 jet in the VM22, when i put the VM18 i was running a 75 jet. since mikuni jets are sized based on fuel flow, its easy math to see that dropping the jet size resulted in a (1-(75/165))= 65% decrease in flow rate through the jet.
now, the speed of the moped didn't decrease much, and it was properly tuned in both scenarios, which means we can assume that mass air flow rate stayed relatively constant and fuel flow rate stayed relatively constant.
so, because mikuni did the hard work for us and linearized the mass fuel flow rate of the jets, the math is really easy to say that (give or take) there was a 65% increase in differential pressure across the main jet to accomplish the same mass fuel flow rate with a smaller jet.
so the differential pressure of having a different float level setting as a percentage change in mass fuel flow rate decreased by a factor of whatever that pressure drop is. if you wanted to just make up some numbers as an example you could say that the main jet delta p on the VM22 was, lets say, 10 cm. So then the 65% increase on the VM18 needs the pressure to to be (10/.45)= 22.2 cm differential to make the same mass flow rate. Now if you are .2 cm off on your float level, on the VM22 that will be a (.2/10) =2 % change in mass flow rate, whereas if you are .2 cm off on the VM18 it will be a (.2/22.2)= 0.9% change in mass flow rate.
I think that math is right but i'm not super sure that you can use the mikuni jet size flow rates in a linear fashion like that, either way it shows a pretty good example of how the original poster is way the fuck wrong.