full tilt MGR question

[captain_swing]

Sometimes my MGR for fulltilt seems low. For example, if I clear $20 in bonus at a full table that means my table has generated $332 in rake (you get 1 point for every dollar of rake and need 16.6 points)and my share should be 332/9=36.8 (and this is conservative because the table won't be full for every hand). If you deduct the 20 in bonus then my MGR should be 16.8. Sometimes it seems like my MGR is around 11-12 for every $20 in bonus I clear. Am I missing anything?

Thanks for the help.