base_opts[:start_date] = case @constructs[wi].wrapper_type
                                     when 2 then base_opts[:end_date].sub_days(@constructs[wi].wrapper_length)
                                     when 3 then base_opts[:end_date].sub_weeks(@constructs[wi].wrapper_length)
                                     when 4 then base_opts[:end_date].sub_months(@constructs[wi].wrapper_length)