I too have noticed this issue, and it does appear to induce a distortion into the final image due to the streching...
Hopefully this is addressed in additon to the sharpening/NR I discuss at http://forums.adobe.com/message/4118159#4118159
Thanks for posting
I believe ACR is doing the correct warp (try using the Fuji desktop raw conversion software ... it should match the ACR result).
The in-camera JPEGs at the short focal lengths actually change the aspect ratio of the image slightly (making it about 3 to 5% narrower), which I think is a glitch. For example, if you take a picture of a square head-on, in ACR it'll be rendered as a square, but the in-camera JPEGs the horizontal side will be about 3 to 5% shorter than the vertical side.
You are right!
Somewhere in the raw process with both silky and ACR converters pixels at each side are discarded. The pixels of about 1 cm of the yardstick (see picture) are not used. The camera's converter does utilise these pixels, BUT squeezes the image to a 0.96 : 1 ratio. This ratio is 1:1 longer focal lengths, the "pixel loss" is then nearly 0.
The pixels might not be output to the raw file or are discarded by the convertors. Perhaps this is done because of quality degradation of corner pixels / coverage at short focal lengths. I'll test to see if it is also related to aperture. NOT an adobe raw issue I should say.
Lower half of image: more pixels at the sides with jpg from camera
Image is squeezed when processed by camera
Original image, 28mm, F2.0