Paul posted about this a few years ago- just search percentages in the "Kallistra's hex based rules" part of the forum.
Here's how he explained it then:
"The percentages for minimum and maximum refer to the total number of units including command units. For example, an army of 20 units including 4 command units, which can have a maximum of 20% heavy cavalry can have up to 4 units of this troop type."
Hope that helps,