I am not sure. I prefer the commandline tool mobigen.exe from Mobipocket. There it is a commandline option.
I currently improve the german translation of the Mobipocket Reader.
Compress eBook file
There must be a combobox somewhere in the options. "Standard compression" is the Palm compression and "High compression" the proprietary Mobipocket compression.
From the commandline help of mobigen.exe it is obvious that it is just a variation of the Huffman compression though.