You're interpreting the graph incorrectly. There's no "bottom of the curve", the graph is showing a distribution, not some property over time. A correct reading

You're interpreting the graph incorrectly. There's no "bottom of the curve", the graph is showing a distribution, not some property over time. A correct reading will e.g. tell you that out of 50'000 requests a total of ~30'000 requests completed in 100ms or less. Or similarly for what you call the bottom of the curve: 5'000 out of 50'000 requests complete in ~25ms or less. This does _not_ state which 5'000 requests that were, and in particular it does _not_ imply that the _first_ 5'000 requests are faster. For this you'd have to plot response time over time.