Hi Luiz;
Not only what Bruce already mentioned ... its also possible that the OLE container has converted the data from UTF-8 to UTF-16 (double-byte) - depending on the Blob data-stream type. So those two things added together can really make a whopping size difference for sure. 
FWIW: I never use OLE containers to manage Blobs in my PB applications.
HTH
Regards ... Chris