It's not at all unusual for DNGs to be smaller file sizes if you did the DNG conversion using lossless compression, did you? Fuji raw files are known for being oversized due to the way they write their image data. Also, totally ignore any findings you may regarding JPEGs, those are lossy compressed and don't figure into the equation...
Hi There Jeff
Thanks for getting back - I'm not worried about the size of the files (they're about 19mb) it's the RESOLUTION which is the issue. i.e 6mp (2900 x 2016) rather than 4000 x 3000
I suspect that it may be a problem with Apple core processing not recognising the files properly, but I'm not certain.
. . . .
Yes, it appears the OS is not aware that there are two mosaic images stored in the DNG (the software should be reading both images, and doing a high-res merge of the data to produce the 12 MP output, instead of just looking at the 1st mosaic image and producing a 6 MP output).