Nick length is not the same as handle length (the handle being what's stored in the bot's user file.) The usual max is 9 chars, although you can change this in the eggdrop.h file and then recompile. As stated in the eggdrop.h file, that would be non-standard and can cause problems with botnets for example, so all linked bots need to have the same HANDLEN set.
BTW, forum mods, I tried to do a search cos I know this topic's been discussed before, but the search feature isn't working, for any thing I tried.