Your spot metering should take in the full spectrum of luminance in the subject, not just one (e.g. from cheeks).
High areas, low areas and then mid-tone areas must be measured, then averaged (spectrals are never spot metered). Incident reading is only useful for directional light.
From the HI/LO/AVG measurement, add or subtract for additional exposure based on testing, not blind conversation. You can make it easier by placing a grey card in the frame and spot meter from that (baseline spot) if you have any doubts, then adjust +/– the exposure through active experimentation. It is entirely possible to create a beautiful portrait without resorting to the depth and breadth of the Zone System.