Correct me if I misunderstood your situation or question. I have three continuous factors, A, B, and C. I want to design an experiment, though, for a model for A, B, and the C to B ratio. Here are the factor definitions:
I can choose any linear model, in this case I included interaction terms:
I ask JMP for 16 runs:
The color map on correlations shows that these estimates are orthogonal:
The lack of correlation is a matter of the model and the number of runs, but I can achieve a balanced design in this case to demonstrate that orthogonality can be achieved. Another column must be added to the data table to determine the factor levels for C in each run.