Local html file can't be loaded.

We are upgrading from cordova-plugin-wkwebview-engine version 1.1.4 to cordova-plugin-ionic-webview 2.5.1
In version 1.1.4, we are using the file protocol to display the local html files.
Using localhost to host files is something that we would like to avoid because our app is generally running under a corporate VPN that by default limits non-standard port access.
After upgrading to 2.5.1, we found that loading a local html page is no longer possible.