The actual blocking rate may vary wildly, depending on the sites you are visting.
Spend a whole day here in the forums exclusively, and 13% would be outrageously high. Spend a whole day googling one term after the other, clicking each sponsored link available, and 13% would be unbelievable low..
It is really hard to supply advice when we know little about your configuration 
But even as Hassio is not a supported environment, the most common reason why you see what you perceive as a low blocking ratio ist that not all your devices use Pi-hole for DNS, and/or not all the time.
This in return can be attributed to quite a number of root causes which may or may not apply to your specific setup (unfortunately, in lieu of a debug token, it is not possible to verify this even for the most common one's only).
Instead of guessing and repeating them here, let me refer you to a rather general reply I've written (on an otherwise unrelated topic).
I think the common ground would be that I am only able to point you in a select few directions where you may be able to learn, better understand and perhaps adjust a few of your network settings so that you may get (or perceive ) better results from your Pi-hole installation.