In days of old, a draw decided who gets to sing when. These days, the producers of the show make up their minds how to present the show.
They base this on having heard the actual songs, and with details of how each country plans to stage their three-minute opus. If someone needs big props, they’ll be better placed after a break or near a song that plans something simple.
Done right, the audience gets a varied musical experience and doesn’t see the creaky bits where the stage hands run about. There won’t be any demands on the hosts to fill (in a language they clearly don’t speak).
This rarely happens.