It's all good - the whole point of a tread like this is to have a discussion.
I have for my personal purposes & pleasure a little PowerPoint where I have quite a few Spydercos all to-scale (to each other), so that I can compare them in life-size on a large monitor. I have attempted to simply scale-down the Caribbean to a 4" total closed length (handle length) - see the photo attached. I would just manage with my very average M-sized with skinny fingers hand to get a full grip.
I have for comparison included the Urban, Para 3 (when not using the choil) and PM2. As one can see, the grip area would be actually a little more than Para 3 (which I confess does not give me full support with thumb on the spine-ramp), a bit less than Urban (which works just fine when using the choil) and somewhat less than PM2 (which works very well for my hand).
Now - we all know, that this is not how smaller/larger versions of a given model are actually designed, but it may give a rough idea.
With the above said - unless changes would be made especially to the butt of the handle (something along the lines of Urban or Chaparral), then 4" closed length would be about as small as I would consider usable even for people with small/medium hands. If one goes any smaller than that, the range of users who could grip the knife comfortably would shrank quickly.
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