Yeah, I'm planning on refilling at a quarter tank or less for consistency. And in those times, that would be easy.
But let's say I take a little road trip and I've already got a full tank of E30. When I fill up, at a quarter tank, that's a 1/4 tank of E30.
If I fill up the rest of the tank with 91, I'm good going back to the 91 tune, even though I would still have a certain percentage of ethanol, right?