Just fyi, the logic needs to be the other way around:

@max_message_size = @members.map do |m|
      m.config['maxMessageSizeBytes'] ?
        m.config['maxMessageSizeBytes'] : DEFAULT_MAX_MESSAGE_SIZE
    end

But this needs to change anyway to allow a min on the result of the map and DEFAULT_MAX_MESSAGE_SIZE will be replaced by DEFAULT_MAX_BSON_SIZE * MESSAGE_SIZE_FACTOR