From my understanding, small changes in IFRs make a lot bigger changes to AFRs than IABs. I'd have thought you still should've noticed a difference though. Maybe there's some thrash in the idle channel somewhere?
IFRs regulate fuel regardless of which position it's in. There are opinions on which is better, but on the carbs I've messed with, I tend to notice more steady AFR readings when the IFRs are in the bottom location.
This is an interesting question. I'd be curious to see what other have to say. I would say since there is an idle circuit and transfer slot on both, the primary and secondary sides on a vacuum sec carb, and they more than likely run off the same idle mixture screws as the primaries, I'd think you would still want at least some of the secondary transfer slot showing at idle. Just thinking out loud on this one...
