Potato starch doesn't help my sleep

I've been experimenting with the relationship between sleep and resistant starch, taking a few tablespoons of Bob's Red Mill potato starch, which some people think improves sleep by feeding the helpful Bifidobacterium that may play a role in producing up to 80% of the body's serotonin.

There’s no question the potato starch raised my Bifido levels:
Sprague Bifido over time

But it seems not to have changed my sleep, either in overall hours:
Sprague Z vs potato starch

or in a more precise measure, like REM:
Sprague REM vs potato starch

You can see from these charts that I did notice some fantastic nights of sleep after starting potato starch, but there were plenty of other nights when my sleep was back to normal and sometimes worse. If I hadn’t measured so carefully, I’d be tempted to overplay the good and underplay the not-so-good. If there’s a psychosomatic effect, then yeah it may have made me feel better, but in terms of actual sleep time, resistant starch doesn’t seem to have helped.