我可以更改纸张和模具上元素的默认大小吗？[Jointjs] [RappidJS]

var paper = new joint.dia.Paper({
  el: $('#paper'),
  width: 800,
  height: 600,
  model: graph
});

var stencil = new joint.ui.Stencil({
  paper: paper,
  width: 200,
  height: 600
});

var customElement = joint.shapes.basic.Rect.extend({
  defaults: joint.util.deepSupplement({
    type: 'custom.Element',
    size: { width: 100, height: 50 },
    attrs: {
      rect: { fill: 'blue' },
      text: { text: 'Custom Element', fill: 'white' }
    }
  }, joint.shapes.basic.Rect.prototype.defaults)
});

stencil.load([{
  type: 'custom.Element',
  size: { width: 100, height: 50 },
  attrs: {
    rect: { fill: 'blue' },
    text: { text: 'Custom Element', fill: 'white' }
  }
}]);

stencil.on('cell:pointerdown', function(cellView, e, x, y) {
  var element = cellView.model.clone();
  element.position(x, y);
  graph.addCell(element);
});