Kinesis Firehose firewall opening for private network HEC

I am trying to use firehose and stream the CloudWatch log to private network (not AWS) HEC. In this case we need to open firewall between two component, as i know firehose is regional based which i cannot get the ip like other component (e.g. MSK i may check the broker IP and use for firewall opening). So how i may resolve this in firehose case? I check in this page

https://docs.aws.amazon.com/firehose/latest/dev/controlling-access.html#using-iam-splunk-vpc

Or i just need to use the ip provided in the page? (e.g. 35.183.92.64/26 for Canada (Central)). If yes, i may have some concern since the IP may changed. if i need to change the firewall rules again once the IP change again?