I just found the probable cause I can’t make it to work:
https://msdn.microsoft.com/en-us/library/windows/apps/xaml/dn792127.aspx
“Note that SuppressSystemOverlays only has this effect on the nav bar if Settings > Navigation Bar > Auto Hide is set on the phone.”
So this is not fixable for all devices unless you ask the user to set it to autohide.
I’m opening an issue for this, sorry for hijacking the thread 