HEPAX File System, file names

[MeindertKuipers]

One of my current little projects is to expand my HP41 disassembler with support for the HEPAX RAM images. With the help of Ángel I now have the details of the files structure. What is lacking is how the file names are coded. According to the available documentation 7 characters are compressed in 6 10-bit words. After some attempts I am still pretty much in the dark as to how this is compressed. It appears that two-bit pairs are spread over the 6 available ROM words, but I fail to see any logic in the patterns.
Next task would be to understand how Register Files are compressed, one 7-byte HP41 register is compressed is 6 10-bit ROM words. Most logical would be if the same compression as the filenames are used, but who knows ...
Does anyone here have any detailed info about this?