I have measured myself quite extensively, and I know that my apexes are about 11 inches apart. Now, on a princess seam garment, the princess line can hit one of two places: directly on the apex or just outside the apexes. So as far as the distance between the apexes, we will use the edge of the princess line to guide us, ignoring the apex marked on the pattern. (I mean, logically different sizes would require the apexes be at different widths.)
So, with an apex distance of 11 inches, I would need at least 6.5 inches for the center piece to be wide enough at the bust. So I will add about an inch or so.
I measured out an inch and did my best to get that line in there without adding a huge arm hole. I don't mind extra at the waist. I will probably need it, but extra in the arm hole would be a nightmare. The extra in the waist can easily be fitted out later.
Consider the princess seam and the apex moved!!
From here, I just followed some FBA tutorial. I also added width at the waist. To be sure, I remeasured all of my pattern pieces again. In the next post, I will reveal the tissue fit result.