Help with FBA larger than D-cup

Wondering how far to spread the cut line for cup sizes larger than D. Do I keep adding 1/4" for each cup size above C? I am a 36G with a 41" high bust and 45" full bust. Would it be correct to make a size 16 and follow the instructions for the FBA by spreading the cut line 1 1/2"? This is my first time sewing a top for myself and doing a FBA.