Marginalia's :line option

I am trying to use the Marginalia gem's :line parameter. It emits something, but it seems to always say 'script/rails:6', as in...

/*application:Realvolve,controller:contacts,action:index,line:script/rails:6:in `require'*/

This is at the top of application.rb:

require File.expand_path('../boot', __FILE__)
require 'rails/all'
require 'marginalia/railtie'

And this is in config/initializers/marginalia.rb:

Marginalia::Comment.components = [:application, :controller, :action, :line]

Do I need to add a permissive regex to include much more of the backtrace so line yields something useful?

Martin