confused ssh tmux interaction

tmux

TL;DR - Solved it.  $HOSTNAME isn't set in interactive shh session

wwalker@polonium:~ ✓ $ head ~/.tmux.conf
#new -s $HOSTNAME
set-hook -g session-created "rename-session $HOSTNAME"
#rename-session $HOSTNAME

# This works:
wwalker@serenity:~ ✓ $ ssh polonium
Last login: Sat Dec  7 12:20:35 2019 from 172.16.16.119
wwalker@polonium:~ ✓ $ tmux
# tmux opens and if there isn't already a session named polonium the new session is name polonium

# This does NOT work
wwalker@serenity:~ ✓ $ ssh -t polonium tmux
# opens tmux but with this error at the top
# /home/wwalker/.tmux.conf:2: usage: rename-session [-t target-session] new-name                                                                  [0/0]