AverageX vs Summarize Field by Average in Pivot Table?

[jbaich]

Hey everyone, pretty new to DAX here so still trying to learn, but I'm curious why I'm getting different results when I use an AVERAGEX function vs the the built-in Summarize as Average function in my pivot table?

The source data table looks like this:

You'll notice that some of the entries don't have time reported. I don't want those to be included in the average. Ie. i don't want it to be dividing 183 WFs Completed by 7.5 hrs, it should be 29/7.5...

I created the following Pivot table with one values column just summarizing the Units Completed/Hr as an Average and another values column where I tried to create a measure using AVERAGEX. As you can see I'm getting different values between the two and just trying to understand why and which one is more accurate. This is my AVERAGEX measure: =AVERAGEX(VALUES('Table1'[Task Completed Date]),'Table1'[WFs Completed/Hr])
This is what my Pivot Table is looking like:

The light blue column headers are the AverageX measure values and the orange column headers are the built in Summarize as Average values. They match on the row context, but the Grand Totals are different at 4.10 and 3.80 and I'm not sure why?

Thanks,
Joe