ahhh, "My Average" is taking the last 25 results into consideration. That's a direct copy of how it's currently done.
This also filters your results by identifier and host. So when you're on Spectrum you'll get an average of only those results, when you're on Verizon you'll get an average of your Verizon results. Same is true if you visit on a desktop, android or iOS. You'll only compare similar results.
But that's only for "My Average" -- the ISP and location are taking into account all results and come from a continuous 15 minute average that runs for all databases. Those numbers constantly fluctuate with the current average user's performance.