I just have a question:

Is the proration of days off a good thing? A fair thing? Is it the right thing to do?

It is my opinion that the accrued vacation is time off awarded with pay that you have earned. Inserting an "adjustment" or proration table has a tendancy to dilute ones vacation value in terms of days off. A reserve with no vacation gets 12 days off. So why doesn't a reserve with a week's vacation get 19 days off?