Could someone tell me why after getting about twenty more best answers, I have stayed at 12 % best answer's ?

It's simple math. Your best answer percentage includes the questions that are unresolved, where the asker has not chosen a "best answer" or where it's in voting. If you continue to answer questions, then your percentage stays the same or drops even if you are winning "best answer" more often.

Look at it this way: you have answered 4 questions and won "best answer" on 1. You have a 25% "best answer" rate. Then you go and answer 6 more questions. Now you have a 10% "best answer" rate even though nobody's won "best answer" on the 9 questions you answered that are still pending (the 3 from before and the 6 you just answered). Your % dropped but it's only because you answered more questions.

Make sense?

Well, if you answered a ton of questions and only 20 received best answers, your percentage won't change a great deal. If you ONLY answered 20 questions and all 20 were best answers, then you would notice a change in the percentage of best answers you've received.

It depends on how many questions you are answering. It is a percentage.

i'm guessing you are getting many answers not chosen as best...