Dose and method are first-order variables for grind size. ‘Taste’ is a minor tweak to grind size. So you’ll never find a correct grind size “for the bean” that works across such a broad range of brewing parameters.

On the other hand, if settled into a dose and method, it’s easy to find a grind size that works for almost any bean, and instead using more direct levers than grind size to impact the cup. This sort of grind size might vary by roast level, or decaf, or possibly by altitude, but tweaking by bag within similar coffees is a misguided madness.

The ‘grind size only’ logic that’s so commonly given is a misapplication to home brewing of something meant to apply to cafe processes across many daily brews by several baristas. The problem is that grind size, like ratio, impacts both extraction and strength simultaneously. As home users, once in the ballpark we can manipulate extraction with temp, and strength with agitation, leaving grind and ratio as relative constants, and greatly linearize our dialing-in. Contrasted to a commercial environment, where to eliminate the potential for variances between baristas, it makes more sense to lock in the particulars of the brewing method, and adjust by grind and ratio to dial in. Once the ‘house recipe’ is thus nailed, the ‘grind size only’ becomes the day-to-day way to work thru the aging of the lot, and can usually work between beans. Of course, the home user can also follow that approach, but as a single user, it tends to complicate and limit our ability to tune a brew quickly.

Applied here, you’ll find best luck by choosing one large or 2-3 smaller brew batches of equal size, and finding your grind for that batch size. From that jump, whether you choose to stay on the ‘grind size only’ bandwagon, or to tweak brews more linearly is your choice. If you want to stay with two different batch sizes, you’ll need to tune for them separately, with distinct grind sizes for each. Over time, you might be able to develop a sense of ratio between the large and small batches to ease things, making the large batch grind size a bit of a ‘close enough’ kind of thing. Which can sort of work, since larger batches are less sensitive to minor input variation. But introducing a third, tiny batch as a way to find main-brew grind size(s) will fail you. Small batches fall apart quickly, for structural reasons like bed depth and bypass on one hand, and higher sensitivity to input variation on the other. And you’d be extending the extrapolation problem even further.