Matt, I believe you're thinking of a Gossen attachment that consisted of a fiber-optic 'wand' that one pressed against the ground glass in order to get a reading. Foolishness, all of it.
I can't figure out why your booster would read a higher reflectance than the spot meter by itself, its usually the other way around. Another possibility that comes is some sort of flare in the optics of the spot meter, but that shouldn't be enough to cause a 1ev difference, and almost certainly not in a consistent way. It may also be, now that I think of it, that the meter is entering a different mode when the probe is plugged in, and perhaps that mode is set to compensate 1ev over reflected direct metering. Just a thought.
All the same, meters disagree all the time. Trick is to have one that is consistent and to trust that it works well all the time. It could be outside ISO spec by 200%, but if its consistent and linear, it wouldn't matter at all.