How big is your terrarium?
they look like they get huge
I am really not sure if you can find a bird of paradise plant less than say 4 feet tall. Unless I'm seriously mistaken. A simple google search or miniature varieties yielded no results
I think the 4ft tall variety is the small version. I have seen a giant type that resembles a large banana tree. (16ft and growing with flowers)
the bird of paradise is a tall fast growing plant that i doubt would do well in anything smaller then a room sized viv
even the smallest species can get to be more then 6ft tall and have leaves more then a foot long.