charlieuk, forgive me, but if I quote you images go uncontrollably in to the quote.
(Laurie, could you look in to that before I sick ex Lacey on to you)
It depends on how / where you line things up for the comparison. (play with the CAD I sent you)
If you line up the handles, i.e. the bit of the board you are standing on upwind or flat, 12'6", 14' (V1 or V2, same plan shape), F16 and 17'4" are very similar a couple of feet either side of where you stand.
The shorter boards get a bit more width to add stability. The longer boards taper more slowly at front and back.
Whether this is just SIC, or every board ever made by anyone I have not established.
Obviously the shorter SIC boards have a closer similarity to each other than when compared to the longer ones.
If you line up the back of the boards, it looks a lot like they started at the back, kept the same plan shape, finished the 12'6' at the appropriate length, then the 14, 16, 17, and finally 17'4 at each length.
Hence the 12'6" is very stubby at the front, the 14 less so. The 16' and 17' boards keep the mid board width longer, with a similar bow / nose plan to the 14'.
But yes, the 12'6" is the 14 with the front cut off. Same applies rocker wise too.
But I / we are probably putting far too much thought in to it.
For me, old, clumsy, and balance challenged, the big boards seem "right".
On the 14, I get a bit of a "where did the front of my board go?" feeling.
On the 12'6", very different. Obviously a smaller board, but after the initial odd feeling (I paddle the 17' boards more than the others) I get a "Hey, this is just right" feeling.
A couple of weeks ago, had strong south easterly wind. I was trying to hide in my usual bay, poke out in to the wind, paddle back up wind in shelter of cliffs.
Out in the breeze, downwinding in basically flat water, the 12'6" was a hoot - heaps of fun. Just "Right". Charging along.
Probably way too verbose answer to a question you didn't ask, but when you do your next Australian trip, bring Area 10, and you, me, Helmy and him can bore each other witless in my garage at Ventnor!
Hidden under the cliffs in shelter
Just off those Red Bluff cliffs in breeze.
Sorry for bum cam angle