If you try to tie them down make sure you water first. It makes the plants more pliable. With that being said do not tie dow any stems other than the main one as this will make your current problem a bigger problem. If you dont want to tie I recommend you use phone book to compensate for height and go for the 12/12. Assumung there is a ceiling you are already getting close to. Also, I've never been s topper so you have to ask one of the other folks.