That's interesting - I have always treated the first 3-6 months as a period to make sure the person is a fit and is ramping at the right speed, and letting them go if there is an issue within that period makes way more sense to me than keeping them on to struggle for a year. It's not a greater red flag for me to see someone got fired two months in than a year and a half in - in fact, the year and a half would cause me to ask a lot more questions.