In a brief survey of web stuff I see a Mobil1 mfg's website that states(automotive myths) if mixing octanes into an empty tank they have different densities & so they say to be certain you do 1/2 into 1/2 to avoid them not mixing. I find that being double talk? It would seem to me that they either mix or they don't? What am I missing? -put "octane" in the search window, then see "automotive myths".
On a Wallace racing site they have a calculator allowing the formula to give desired final octane from whichever octanes based on total capacity. No further mention of what if stuff there.
It's also hard for me to imagine a bike tank not agitating the fuel enough to mix it , no matter the empty vs. 1/2 full idea.