HISTFILESIZE is kind of a misnomer. It's the maximum number of lines in HISTFILE, where HISTSIZE is the maximum number of commands. If you have HISTTIMEFORMAT

HISTFILESIZE is kind of a misnomer. It's the maximum number of lines in HISTFILE, where HISTSIZE is the maximum number of commands. If you have HISTTIMEFORMAT set, then each command gets at least 2 lines, plus the possibility of multi-line commands.