Add a newline if the prompt is too long

Created by: Rmano

Shell: zsh Operating system: linux Ubuntu 18.04 Liquid Prompt version (tag, commit): 5f4aeece

I am trying to add a newline to the prompt only if the characters left are less than, say, 30. In plain zsh you can use the %-30 prompt directive, so I tried

export LP_PS1_POSTFIX=$'%-30(l:\n> :)'

...but it is doing nothing. Is there a correct way to do this?

Thanks for the nice software!