Ralph is absolutely right about shadow placement, in that with a spot meter, it is a guess. This is true because a zone is a range of tones not one tone. The high end of zone III and low end of zone IV are almost indistinguishable.
There are three concepts to remember here:
1-is that, our gear, our eye, our subjects, our style, et cetera... are different than Ralph's. All those differences affect what works best for the rest of us. We each need to test our whole system and see what works best for us and come up with our own EI.
2-is that we can factor in anything we please into our personal EI. The placement change Ralph speaks of can be factored in by changing the EI we dial into our meter. Use 200 instead of 400 for example to affect the same change.
3-is that most all the guess work is eliminated when you use a known target to meter from, like Bill suggested above by metering off his hand. This is a practical equivalent of incident metering.