FiddlerCore with Selenium proxy settings

Question

I use FiddlerCore to capture HTTP traffic when performing web UI tests with Selenium (C#) ChromeDriver. I have finally managed to get it working by trial and error, but need a hint on why my solution works and the logical way (for me) doesn't.

I configure the fiddler proxy as:

CONFIG.IgnoreServerCertErrors = false;

FiddlerApplication.Prefs.SetBoolPref("fiddler.network.streaming.abortifclientaborts", true);

var startupSettings =
    new FiddlerCoreStartupSettingsBuilder()
        .ListenOnPort(0)
        .DecryptSSL()
        .OptimizeThreadPool()
        .Build();

FiddlerApplication.Startup(startupSettings);
HttpPort = FiddlerApplication.oProxy.ListenPort;
FiddlerApplication.Log.LogFormat("Created HTTP endpoint listening on port {0}", HttpPort);

secureEndpoint = FiddlerApplication.CreateProxyEndpoint(HttpsPort, true, Host);
if (secureEndpoint != null)
{
    HttpsPort = secureEndpoint.ListenPort;
    FiddlerApplication.Log.LogFormat("Created secure endpoint listening on port {0}, using a HTTPS certificate for '{1}'",HttpsPort, Host);
}

CertMaker.trustRootCert();

This basically follows the demo project provided for FiddlerCore. Note, that the proxy is not registered as system proxy.

Then, ChromeDriver is configured as:

var chromeDriverService = ChromeDriverService.CreateDefaultService();
chromeDriverService.HideCommandPromptWindow = true;

var options = new ChromeOptions();
options.Proxy = new Proxy()
{
    HttpProxy = $"{SkicoProxy.Host}:{SkicoProxy.HttpPort}",
    SslProxy = $"{SkicoProxy.Host}:{SkicoProxy.HttpPort}"
};
_driver = new ChromeDriver(chromeDriverService, options);

What doesn't work, although I would expect it to is:

options.Proxy = new Proxy()
{
    HttpProxy = $"{SkicoProxy.Host}:{SkicoProxy.HttpPort}",
    SslProxy = $"{SkicoProxy.Host}:{SkicoProxy.HttpsPort}" // HTTPS PORT INSTEAD HTTP PORT
};

Still, if I do not configure the endpoint in Fiddler, SSL websites are shown as unsafe in Chrome.

Why doesn't SSL traffic needs to be routed through the according endpoint and why does it even work if it is not proxied through the secure endpoint?