Matter manual step()

Phaser 3
1

I’m using matter for physics and using a manual step( [delta] [, correction]). However, changing the delta doesn’t seem to change the amount of time the physics steps. I’m wondering if this is expected behaviour (ie it is always locked to real time and this is just the step time) or if I am missing something else. Example code below:

var config = {
type: Phaser.AUTO,
width: 800,
height: 600,
backgroundColor: '#000000',
physics: {
    default: 'matter',
    matter: {
        gravity: { x:0, y: 0 },
        debug: false
    }
},
scene: {
    preload: preload,
    create: create,
    update: update
},
fps: 60
};

var game = new Phaser.Game(config);

function preload ()
{
this.load.image('player', 'assets/images/phaser-ship.png');
}

function create ()
{
  this.matter.world.setBounds(0, 0, 800, 600);
  this.player = this.matter.add.image(400, 100, 'player');
  this.matter.add.image(400, 200, 'player');

  this.matter.pause();

  this.cameras.main.startFollow(this.player);

  this.player.setAngularVelocity(0);
  this.player.setVelocity(1, 0);
}

var step_size = 1;

function update (time, delta)
{
  this.player.setVelocity(1, 0);
  this.matter.world.step(step_size);
  step_size = step_size + 5;
}