Ahh, so many variables...I was hesitant to post these specs because design-by-message board can become frustrating!
But seriously, I do appreciate the insight, as various comments have prompted questions to the framebuilder, all of which he's explained to me in detail--from effect on hip placement to handling dynamics.
Long story short, the builder has a bunch of measurements from my wife and I, and this is what he's putting together based upon those measurements. I trust him.
I don't want to become "that customer" mentioned in a prior Competitive Cyclist blog (where he explained why he had to stop carrying Pegoretti's)--you know, the one who asks a thousand questions of their builder (actually, in CC's case, the question went from customer to CC to importer to Pegoretti, and who knows what got lost in translation).
Standard issue tandems are probably spec'd the way they are to meet the middle of the bell curve, and the expert shop works on fitting riders around that standard spec. In this case, I submitted measurements, communicated my intent, and now I just need to sit back and relaaaaax....
I can better spend my time learning about tandem parts & accessories and how they work.
Cheers.