The following settings will tighten the ssh jail in fail2ban. Add (or edit) the following lines in /etc/fail2ban/jail.conf:
[ssh]
enabled = true
port = ssh
filter = sshd
logpath = /var/log/auth.log
maxretry = 6
# set findtime to 1 day
findtime = 86400
# set bantime to 1 day
bantime = 86400