I’m not aware of any differences between Free and Pro apps as far as how statistics are currently measured. If it’s been more than 30 days and several users already have the app installed, the number may very well get smaller. Again, I’m not exactly sure how it all works as I have not seen any good documentation on it other than the link I shared with you. All I know is that is has something to do with unique devices.
I found another older comments: