Affiliate + MarketPress: Can't seem to work

My MarketPress is network enabled.

When the MarketPress add-on is activated, you’ll see a new Affiliate Settings section in the Accordingly the to the document, it says that I can add in the commission amount this way:

MarketPress settings at Products > Store Settings > Payments.

Enter a value for the Set percentage to be paid to affiliates option to credit affiliates a percentage of the referrals they make resulting in MarketPress product sales.

But in my system, there's no option to include the affiliate percentage. It seems to only work for Pro Site?