Question about feudal aristocracy xp gains

I keep seeing that units gain xp whenever their liege lord gains renown, but how exactly does that work? Does the xp gain scale based on how much renown is earned or am I better off going for as many seperate instances of renown gain regardless of the total renown gained? Can I keep getting the xp after my liege lord gets to it's tier 4 renown rank? I keep looking for more details on the liege lord mechanic but can't find any specifics anywhere.