Example of how to reproduce rails_admin issue #2627

rails_admin_subclassed_sti_model.rb

# == Schema Information
#
# Table name: companies
#
#  id                 :integer          not null, primary key
#  name               :string(255)      not null
#  type               :string(255)      not null
#  created_at         :datetime
#  updated_at         :datetime
#

class Company < ActiveRecord::Base
end


# == Schema Information
#
# Table name: companies
#
#  id                 :integer          not null, primary key
#  name               :string(255)      not null
#  type               :string(255)      not null
#  created_at         :datetime
#  updated_at         :datetime
#

class Client < Company
  before_create :set_generic_type

  private

  # Sub-classed models set the type to Admin::[User Type]::Client instead of
  # simply Client
  def set_generic_type
    self.type = 'Client'
  end
end


module Admin
  module SuperUser
    class Client < Client
      # By default, where would include "type = 'Admin::SuperUser::Client'"
      default_scope { rewhere(type: 'Client') }
      
      rails_admin do
        list do
          field :name, :show_link do
            searchable :name
          end
        end

        show do
          field :id
          field :name, :show_link
        end

        edit do
          field :name
        end
      end
    end
  end
end

module Admin
  module Reseller
    class Client < Client
      # By default, where would include "type = 'Admin::Reseller::Client'"
      default_scope { rewhere(type: 'Client') }

      rails_admin do
        list do
          field :name, :show_link do
            searchable :name
          end
        end

        show do
          field :name, :show_link
        end

        edit do
          field :name
        end
      end
    end
  end
end

Example DB migration

class CreateCompanies < ActiveRecord::Migration
  def change
    create_table :companies do |t|
      t.string :name, null: false
      t.string :type, null: false

      t.timestamps
    end
  end
end

I had to explicitly subclass from ::Client, or Rails admin gave me a "Circular dependency detected while autoloading constant Admin::Reseller::Client".

module Admin
  module Reseller
    class Client < ::Client
...

I'll let you know what else I'm able to figure out.