To my way of thinking, if there were an allowance for width, there would be no reason to have a Wr chart in the first place. I use a Wr chart not as a calculator to estimate my fish's weight, but as a tool to show my fish's deviation from what would be considered a healthy average weight for the species in general.
There needs to be a variable in the formula in order to form a comparison...I think that's where width, expressed as weight most often, enters in.
If width is incorporated into the formula, then what shall we use as a variable? Density of flesh, or mass of internal organs?
If it becomes a case of plugging in the numbers, ALL the numbers, (X+Y=Z), then what constitutes the difference or discrepancy if no two fish of the same measurements don't weigh exactly the same?
Just some random, early morning thoughts.