I've had users start over registering index fingers and thumbs from each hand. That seems to be a great way to have it work when you grab the phone from a pocket and hold in many ways. I ask them to be aware of the press and tap differences for home screen vs Apple Pay. This has taken people from thinking it is ineffective to useful.
I work with 3 X owners. I see face ID works for the most part but I also see my having those 2 on each hand fingers set up lets me use the phone fast, and I have no problems with helmets, googles, and use during action sports.
I'm not really against or for face vs fingers as many are but I sure get a lot of utility with my current setup. It worked on my 6, and the technology has been as or maybe more reliable - probably just faster - with the 6S Plus and my 7 Plus.
I digress, but the 7 Plus phones seem so good that it is hard for me to rationalize an X when the second generation of face ID may well jump in performance like second generation of touch ID.