How do I geo-search multiple models with ThinkingSphinx?

define_index do
    indexes [:first_name, :last_name], :as => :name
    indexes login
    indexes email
    indexes headline
    indexes description
    indexes business.name, :as => :business_name
    indexes [addresses.street_1, addresses.street_2, addresses.city, addresses.postal_code], :as => :address

    has created_at, :sortable => true
    has addresses.latitude, :as => :latitude, :type => :float
    has addresses.longitude, :as => :longitude, :type => :float

    set_property :delta => true
  end

define_index do
    indexes title, :sortable => true
    indexes description
    indexes [address.street_1, address.street_2, address.city, address.postal_code], :as => :address
    indexes images.title, :as => :image_titles
    indexes images.description, :as => :image_descriptions
    indexes categories(:name), :as => :category_names

    has price, :sortable => true
    has created_at, :sortable => true
    has address.latitude, :as => :latitude, :type => :float
    has address.longitude, :as => :longitude, :type => :float
    has categories(:id), :as => :category_ids

    where "`items`.`state` = 'for_sale'"

    set_property :delta => true
  end

ThinkingSphinx::Search.search('keywords',
  :geo => [
    degrees_to_radians(params[:lat].to_f),
    degrees_to_radians(params[:lon].to_f)
  ],
  :latitude_attr  => "latitude",
  :longitude_attr => "longitude"
)