The problem here is with the math. Chen, You are looking at the final dry weight as a variable, and you are looking at the moisture as a constant. The dry weight is a constant (because when nothing else can leave the material as it dries, the mass becomes stable). The moisture is the variable. Because the plants have varying amounts of moisture in a continuing cycle, you will always get different percentages.
There is a correlation between wet and dry weight, but because that correlation is due to the variable of moisture present, the correlation is nonlinear and worthless as a measure of productivity.
I know that's splitting hairs but I believe that's the mechanics of it.
The bottom line: wet weight versus dry weight is not a viable form of measure of how well the final yield will be