That’s not a big surprise, only 16% of your fans actually see your Page Posts. That’s not a lot but you don’t have the choice anyway.
You can check your edgerank here. Sometimes you get a higher pourcentage of people seeing your Page Posts. It really depends on the type of content you publish and the Page you are promoting. For example I am managing a page on Facebook who gets more than 40% attention because I only have qualified fans.