How should iOS Webview Scaling work?

I downloaded the iOS (non-Forms) Loading_a_web_page example, which loads Xamarin.com. When testing it, if ScalesPageToFit is true then the entire width of the web page fits in the simulator's screen; if it is false the width of the page is larger than the screen. If I change the url to my web page it works the same way.
Then I switched to FormsGalary and changed the url to xamarin.com. When I test that, the web page is scaled to fit on the screen; when I change the URL to my web page it is not. I added a custom render and added ScalesPageToFit = true, but that had no effect, the web page is still too large for the screen. I switched the url back to xamarin.com and changed ScalesPageToFit to false, but the page is still being scaled to fit. I also tried the url http://developer.xamarin.com/recipes/ios/content_controls/web_view/load_a_web_page/ and it works the same way my page does - it does not scale regardless of the ScalesPageToFit setting.
How should this work, and do I need something on my web page to get it to work?