It seems that with greater R value, and hence less heat flux/greater efficiency, the dew point moves more interior through the wall assembly. Is the goal keeping the dew point out of the insulation that will support mold growth, ie fiberglass?
Is there a role for a vapor barrier in the pony wall, to keep interior/moist air out?
Say, a wall construction like this:
sheath / FG / poly / sheath / FG / interior gypsum/ latex paint
(The interior sheathing is a requirement for seismic stability, per Seattle Project Impact, to provide bracing of the pony wall against racking in and earthquake.)