Understanding implementation of OPC UA Subscription service

I was trying to understand the architecture for OPC UA “Subscription” service implied in Visual Components. When I see the settings for “Server to Simulation” and choose update mode from cyclic to event-based, I believe i am changing from “Read” service to “Subscription” service.
I see parameters like Sampling Interval, Publish Interval and Queue Size.
If my understanding is correct,
Sampling Interval : the time interval of sampling the MonitoredItem by the server
Publish Interval : the time interval at which the Subscription executes and attempts to send NotificationMessage to the client
Queue size : if sampling interval is faster than publish interval or there are no PublishRequest from the client, the NotificationMessage need a queue before they are acknowledged

My curiosity is in the parameters setting the PublishRequest rate (how often this PublishRequest is sent by client) parameter for client seems to be lacking. The NotificationMessage is only sent if PublishRequest is available and Publish Interval is just utilized to check if this request is there or not by Subscription. (As per OPC 10000-4 page 73 Subscription Model)
Is this parameter auto set? i am just trying to understand how things are implemented.

Any leads would be much appreciated.

I think that same “Publish interval” value is used for both such that the server can send the notifications at that set rate if there are any to send.

VC uses Unified Automation’s SDK for the OPC UA client. This is what their documentation says: