ClientAck behavior in case ack is not sent (timeout)

Hello everyone,
I'm trying to implement the transactional client with timeout-based delivery in Solace leveraging the ClientAck mode but I'm struggling to understand what is the timeout setting used by Solace to redeliver a message in case the consumer that receives the message does not send the Ack within a specified time.
The scenario I'm working with is a pool of X .NET Core consumers subscribed to a non-exclusive durable queue in which a producer publishes persistent messages.
Consumer queue setup:

IQueue queue = ContextFactory.Instance.CreateQueue(queueName);
                Flow = session.CreateFlow(new FlowProperties()
                {
                    AckMode =  MessageAckMode.ClientAck ,
                    AckTimerInMsecs = 500,
                    MaxUnackedMessages = -1,
                    WindowSize = 1 //set a persist message as one unit
                },
                queue, null, HandleMessageEvent, HandleFlowEvent);
Flow.Start();

// block the current thread until a confirmation received
WaitEventWaitHandle.WaitOne();

//dispose flow then restart the flow in the next loop
Flow.Stop();
Flow.Dispose();
GC.Collect();

Here the consumer code in which I added a "sleep" to simulate an high processing time. I expect at some point the message to be redelivered to another instance because the Ack has not been sent within N seconds:

 // Received a message
Console.WriteLine("Solace: Received message.");
using (IMessage message = args.Message)
{
   var msg = 
   Encoding.UTF8.GetString(Compression.Decompress(message.BinaryAttachment));
   // process the message
   Console.WriteLine("Processing message.. Is redelivered: " + message.Redelivered);
   MessageEventHandle(message.Destination.Name, msg);
   // process completed, we can Ack
   if (Flow != null)
   {
      // to test how long it waits before redelivering to another consumer
      Console.WriteLine(string.Format("Wait {0} millisec before sending ack", _delayMillisec));
      Thread.Sleep(_delayMillisec);
      Flow.Ack(message.ADMessageId);
      Console.WriteLine("Message Ack at " + DateTime.Now.ToString());
   }
}

I executed this code changing the _delayMillisec to simulate short and long processing times.
By running those experiments I was able to determine that:

• when the processing completes in less than 20 seconds the message is not redelivered to another instance
• when processing takes more than 30 seconds the message is always redelivered to another instance
• between 20 to 30 seconds it's inconsistent: sometimes it's redelivered sometimes not.

In summary this experiment shows that the internal timeout setting that Solace uses to decide when to redeliver a message is somewhat between 20 to 30 seconds.

However I was not able to find this number in the documentation nor where I could change it.

Could you please clarify how Solace decides when to redeliver the message when ClientAck mode is enabled in case the Ack is not received? Is it by a fixed timeout or is there any different logic it gets applied?
If it's by fixed timeout, can this setting be changed and how?

Thanks,
Daniele