I have a 32GB SxS card from a Sony EX1 (XDCAM EX.)   The card is nearly full--31 gigs of almost 2 hours of footage.   I linked by AMA and then transcoded the footage to DNxHD 145.   The resulting Avid MediaFiles are 119 gigs...almost 4 times the size of the original footage.  

Why are the transcoded Avid MediaFiles so much larger than the original (long GOP) files on the SxS card?   Since DNxHD is a relatively efficient codec, I would have thought it would have been the other way around???

As a test, I exported the files from the SxS card using the Sony Browser.  (Export MXF for NLE).   The resulting file exports are the same size as the files on the card--31 gigs. 

Terry:

I guess your clips on the card use the XDCAM codec with 35MBit/sec, other variants use 50MBit/sec (HD 422).
Your AMA transcoded files use DNxHD with 145Mbit/sec.

145 : 35 =  4,14

But: did you expect anything else??
You could consolidate your SxS card - the size would be the same because the codec would be the same - like your attempt with the Sony Browser.