How should widgets be resized in npyscreen (a Python curses wrapper)?

Question

I want the height of some widgets in my npyscreen app to resize as the terminal is resized.

Specifically I want those two column widgets to continue to take up about the same fraction of the height of the terminal when the terminal is resized, with the row widget at the bottom to stay at the bottom of the terminal when the terminal is resized.

I've got something sorta working but when the terminal gets resized something is going wrong with the rendering overall, like the widgets don't know where I want them to be drawn. What might be going wrong? How should this be done properly?

import curses
import sys

import npyscreen
npyscreen.disableColor()

def main():
    app = App()
    app.run()

class App(npyscreen.NPSApp):
    def main(self):
        form = npyscreen.FormBaseNew(name = "COMMUNICATIONS")
        column_height = terminal_dimensions()[0] - 9
        widget_contacts = form.add(
            Column,
            name       = "CONTACTS",
            relx       = 2,
            rely       = 2,
            max_width  = 20,
            max_height = column_height
        )
        widget_messages = form.add(
            Column,
            name       = "MESSAGES",
            relx       = 23,
            rely       = 2,
            max_height = column_height
        )
        widget_input = form.add(
            npyscreen.BoxTitle,
            name       = "INPUT",
            max_height = 5
        )
        widget_input.resize
        widget_contacts.values  = ["alice", "bob"]
        widget_messages.values  = ["2018-09-19T2001Z    a message", "2018-09-19T2002Z    another message"]
        widget_input.values     = ["sup"]
        #exit_button = form.add(
        #    ExitButton,
        #    name       = "EXIT",
        #    #relx       = 78,
        #    rely       = 23
        #)
        widget_contacts.max_height = 5
        form.edit()

class Column(npyscreen.BoxTitle):
    def resize(self):
        self.max_height = int(0.73 * terminal_dimensions()[0])

class ExitButton(npyscreen.ButtonPress):
    def whenPressed(self):
        sys.exit(0)

def terminal_dimensions():
    return curses.initscr().getmaxyx()

if __name__ == "__main__":
    main()