So I took the calipers to the new-to-us EB-4 and the Kingfisher and Kestrel, to see how much smaller the EB-4 neck dimensions were, giving such a noticeable easier feel, especially frets 1-4 or so.
What sorcery is this! The EB-4 neck is bigger, noticeably, than the current SEs! 1.63" wide vs 1.59" at the nut. About 1/8" thicker, too (hard to measure with strings on): 0.825" vs 0.712" wood thickness (i.e. ignoring the fret height) between the first fret and nut, eyeballing using calipers.
We then picked them up, and lo and behold, the EB-4 still feels "easier" to wrap our hands around, even though it is physically bigger in those two dimensions. Maybe the "roundness" of the neck profile - perhaps the SEs are more "D" shaped, whereas the EB-4 is more "C" shaped?
Admittedly my wife had been playing our bandmates Yamaha bass the night before, so maybe the EB-4 was such a difference it threw off her now mis-calibrated hands, and just felt easier, but we did do a direct compare in feel with the Kingfisher we had brought along with the EB-4 (in case the unopened EB-4 was somehow broken).
Maybe it is the maple? I have always felt that maple was more comfortable in my hands. This isn't the satin unfinished-feel maple of today's PRS (which is the best maple finish ever, IMHO), this still has a light "lacquer" to it.
Gonna try to do some playing comparisons later today, for neck feel and tone. Should be illuminating!