I double checked how wordpress works and indeed they have no real usergroups.
As stated I know an administrator is user level 10 meaning that is how we know you are an admin. Using your site as a guide this is what I found
Subscriber is 0
Contributor is 1
Author is 2
Editor is 7
Admin is 10
Therefore in Photopost I expanded upon the groups and this is now how we do it
Contributor is 1
Author is 2
Subscriber is 3
Guest is 4
Editor is 7
Admin is 10
You can look at your usergroups in photopost to see what I did for you. That might eleviate some of your confusion. The problem is when dealing with a product that has no usergroups we usually just make our own but no big deal I can match them to post roles it makes no difference.