I wasn't able to get the same answer as what was provided in the start file but when I downloaded the supplied solution and ran it, I got the same output as what I'd been seeing in my solution.
Not sure if the data changed but I got 0.146740511271132
I learned a lot from this one because I don't have much experience with batch macros. I had to look at other examples and cheat a bit first but it was well worth the effort because it really cemented how to make this work. Also, in case it helps anyone, I learned that when you put a macro to read multiple files into your workflow, it will only show the first line of data until you put another tool in the workflow after it. I beat my head against the wall for a while on that one!
Here is my macro:
Here is my workflow:
And here is the solution: