Understanding ROS 2 publisher size, subscriber size, and topic size

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(I asked this question in robotics.stackexchange.com but did not received any answer! That is why asking in here with some modifications.) I have the following ROS 2 scripts for a publisher node:

import rclpy
from rclpy.node import Node
from std_msgs.msg import String
import time
class MinimalPublisher(Node):
    def __init__(self):
        super().__init__('minimal_publisher')
        self.publisher_ = self.create_publisher(String, 'topic', 1)
        self.timer1 = self.create_timer(1, self.timer1_callback)
        self.timer2 = self.create_timer(2, self.timer2_callback)
        self.timer3 = self.create_timer(3, self.timer3_callback)
        self.i = 1
        self.j = 1
        self.k = 1
    def timer3_callback(self):
        msg = String()
        msg.data = 'timer3:  %d' % self.k
        self.publisher_.publish(msg)
        self.get_logger().info('Publishing: "%s"' % msg.data)
        self.k += 1
    def timer2_callback(self):
        msg = String()
        msg.data = 'timer2: %d' % self.j
        self.publisher_.publish(msg)
        self.get_logger().info('Publishing: "%s"' % msg.data)
        self.j += 1
    def timer1_callback(self):
        msg = String()
        msg.data = 'timer1: %d' % self.i
        self.publisher_.publish(msg)
        self.get_logger().info('Publishing: "%s"' % msg.data)
        self.i += 1
        # self.create_rate(4).sleep()

def main(args=None):
    rclpy.init(args=args)
    minimal_publisher = MinimalPublisher()
    time.sleep(2)
    msg = String()
    msg.data = 'Publishing garbage 1'
    minimal_publisher.publisher_.publish(msg)
    msg = String()
    msg.data = 'Publishing garbage 2'
    minimal_publisher.publisher_.publish(msg)
    msg = String()
    msg.data = 'Publishing garbage 3'
    minimal_publisher.publisher_.publish(msg)
    msg = String()
    msg.data = 'Publishing garbage 4'
    minimal_publisher.publisher_.publish(msg)
    msg = String()
    msg.data = 'Publishing garbage 5'
    minimal_publisher.publisher_.publish(msg)
    msg = String()
    msg.data = 'Publishing garbage 6'
    minimal_publisher.publisher_.publish(msg)    
    time.sleep(3)
    # rate = minimal_publisher.create_rate(5)
    # rate.sleep()
    try:
        rclpy.spin(minimal_publisher)
    except KeyboardInterrupt:
        pass    
    # minimal_publisher.destroy_node()
    # rclpy.shutdown()

if __name__ == '__main__':
    main()

I used timer to hold after publishing some garbage messages, and then started spinning using 3 timers. I have a simple subscriber node as follows:

import rclpy
from rclpy.node import Node
from std_msgs.msg import String
import time

class MinimalSubscriber(Node):
    def __init__(self):
        super().__init__('minimal_subscriber')
        self.subscription = self.create_subscription(String,'topic',self.listener_callback, 4)
        self.subscription  # prevent unused variable warning

    def listener_callback(self, msg):
        self.get_logger().info('I heard: "%s"' % msg.data)

def main(args=None):
    rclpy.init(args=args)
    minimal_subscriber = MinimalSubscriber()
    # delay = minimal_subscriber.create_rate(2.5)
    rclpy.spin(minimal_subscriber)

if __name__ == '__main__':
    main()

I used a launch file to run both publisher and subscriber at once. I did some experiments by varying the publisher and subscriber queue size in the above code in order to understand topic size, publisher queue, subscriber queue as follows:

Experiment 1: pub queue size 1, sub queue size 1. Results: Only the 6th garbage message is shown. After that every message is received from all 3 timers (5 garbage messages lost)

Experiment 2: pub queue size 100, sub queue size 1. Results: EXACTLY SAME AS EXPERIMENT 1 (also checked for pub size 10, 5, 6 and results are same)

Experiment 3: pub queue size 1, sub queue size 100. Results: All 6 garbage messages are shown (nothing lost). After that every message is received from ... (more)