This nickname length setting, in the config file is not what you need. This setting tells eggdrop what size nicknames to expect, and not what size handles you wish to use for the bot, or for user handles on the partyline.
To do this, you will need to re-compile.
Download the source code and de-compress.
Edit the file src/eggdrop.h
Change the line reading
#define HANDLEN 9
Change the 9 to the size your network supports.
Now just use "./configure", "make" and "make install" as usual.
note: If you do this, and are linking bots in the partyline, then every other bot will have to be done to match the same setting, else the bots will not link.