Filter through relationships

I've got the following component:

export default Ember.Component.extend({
  frontLayers: function() {
    return this.get( 'layerColours' ).filterBy( 'layer.aspect.angle', 'Front' );
  }.property( 'coordinate.@each.layerColours' )
});

Where layerColours has one layer and it has one aspect with an angle property.

The problem is the filtering doesn't work. Debugging the return value in the console just gives me [_super: function, nextObject: function, firstObject: Object, lastObject: Object, contains: function...]

If I remove the filterBy I get the layerColours no prob.