Rating and voting systems have meaning only if they have structure, and if folks use that structure in their rating/voting strategy. If you fail to work with the structure, that will result in your votes meaning less.
In this case, the behavior you're describing is exactly the stuff that makes your votes have less meaning in the structure. You give an XP because you really like one post. You see another post by the same person, and want to give another XP. So, you lay about you to "burn through the buffer" as you put it. In that process, you devalue your first point. So, why in heaven's name are you doing that?
The system is currently designed to show breadth of appeal, not depth. You already said you liked the person's post. That you like seventeen other of their posts is not really what the system is measuring - you liked the one, we already know you're going to tend to like other posts by that same poster.
If a person has 20 XP now, it more or less means that his posts were liked by something like 20 people. That five people liked him a whole lot is not something the system is intended to display. Trying to force it to display depth when it isn't intended to is what makes your votes have much less meaning in the system.