In most brands and models, there is no difference in a 28.0 and 28.5. If you are taking out the stock sock liner and replacing it with a custom footbed or trim to fit footbed, there will be no difference in the snugness of one vesus the other.
For the business to be profitable for the boot companies, they build the fewest number of shells and parts of shells. Mondo point sizing allowed the boot companies to reduce the number of lower shell and upper cuff molds to make a size run. There was a time when there were differences in liners and insoles, but that has slowly gone away.