That may be the case; however, contribution is a very broad term. Again, when I am looking at contribution, I want to see how the player involves their character in the storyline. How is that character helping the party out? Every action the character takes impacts the game in some way, and those actions are their contribution. They have to be considered.
I have a couple of players like this in my group as well. But when they finally speak up, they always use their character in a manner that improves upon the narrative of the story, and this is what I award experience for. They can spend huge parts of the session being quiet and introverted, but contribution doesn’t have to mean involvement in the conversation. It should be a determination of how well the character benefits the party.
I would never suggest putting a player or her/his character on the spot. That is a sure fire way to make them uncomfortable and possibly push them to quit. Evaluating their contribution doesn’t have to mean spotlighting them in anyway.
Aren’t those contributions? Shouldn’t they be rewarded for doing that?
It’s not about leveling faster, it’s about encouraging active participation and involvement in making the story a success. My campaigns aren’t about combat. Most of the time, there is a creative non-combat solution to every scenario. If someone in the party figures that out, and takes that path, they get more exp than those that attempted to fight it out instead.
Okay I may have misunderstood. You're less rewarding active and spotlit participation, and more rewarding baseline participation. It wasn't that you had party members that weren't being loud and sociable, you were dealing with players who were actively doing nothing to help the group. I see your predicament. That particular issue didn't even graze my mind because I've literally never seen that happen on a table.. It also seems that your bonus exp isn't breaking too high on the experience scale. What's the most bonus exo you've handed to someone on a session?