To better assist on this, could you please confirm if you have hosted the WebApp(website) on an Azure VM or App Service WebApp? Could you please share any blog/Azure doc on the changes you’re referring to for subnet and IP address size?
For regional VNet on App Service - The feature requires an unused subnet that's a /28
or larger in an Azure Resource Manager VNet.
Just to highlight on App Service, the VNet Integration depends on use of a dedicated subnet. When you provision a subnet, the Azure subnet loses 5 IPs from the start. One address is used from the integration subnet for each plan instance. If you scale your app to four instances, then four addresses are used. The debit of 5 addresses from the subnet size mean that the maximum available addresses per CIDR block are:
/28 has 11 addresses
/27 has 27 address