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You just about have me convinced, but I can't admit that you're right until
I find the error in my way of doing it. This will have to wait until I'm
both well-rested *and* in a proper frame of mind. 

Presuming you're right, you have my deepest thanks. 

My confirmation of my error and your correctness is on my to-do list.

Once it's confirmed, I'll have to rewrite the 'Revisiting the zFF' page
because the error is large enough to make a difference in the evaluation of
the piece. My evil twin would curse you for it, but I am above all that. 

Evil twin. Hmmm. Evil Twin Chess. James T. Kirk's evil twin was from an
alternate universe, so a two-board setup reminiscent of Alice's Chess seems
natural. Same move on both boards, all is well. But the N and its evil twin
must have different powers of capture or movement; when you make differnt
moves, what's the rule to make it a playable game? Why of course! you have
to move both the Q and her evil twin, unless one of the two has been
captured! Mate on either board wins. The army: N twins with Fibnif, B twins
with fBbN, R twins with mRcHcWcD, Q twins with Chancellor, K twins with K,
P twins with berolina P. No playtest but I'll bet it works with at most one
more rule needed somewhere.