What is the drop rate for g13 finishers?

This is an example where I ran 31 sims and was granted 1 item of gear. I've been simming these mk12 gear nodes for about a week and the drop rate is terrible. I read it was 20% but I never get anywhere near that, and never get sims where I get more than supposed odds so it balances out. 

I've ran 30-40 every day and have never had more than 3.