The darker the roast, the lighter a bean should be. You could count a number of beans you have your numbers right and get decent results with, weigh them, and thus compare their roast to that of other beans. That way you‘d be able to find out if your achieved ratios are tied to the roast. Maybe you could even work out a scale telling you what to expect, a ballpark to get your ratio somewhat right when opening a new bag of beans.

That said, I’m only citing theory here, don’t take what I say as the last word on anything :)

It might help to know a little more about the actual beans. Depending on the roast those ratios might indeed vary greatly, I’d think.