Average monthly attendance

This seems like it should be very simple, but I'm clearly doing something wrong because my average monthly attendance is coming back as 1 for nearly every month. I'm trying to put together a widget to look at average monthly attendance for our museum admissions. I have one for daily averages and it works, but when I try to change it from daily to monthly something isn't working. This is the one that isn't working:

And this is the daily one that is:

I feel like I'm missing something really obvious on this one. Does anyone have a widget for average monthly attendance and can provide some insight?

Thanks!
Anne