+1, incidental reading from under the chin pointing the meter at the camera position, and take the damned shot before the sitters eyes glaze over from boredom, the sitters facial expression is so important in portraiture, and I see so many portraits that are are shot as if they were inanimate objects like still lifes , or landscapes.
For years I just calculated the exposure from the guide number of the flash. It's simple and instantaneous. Some adjustment to the exposure might be necessary when part of the subject is illuminated by two or more flashes, but that can be learned through experience or calculated with basic math.
With an incident meter you do the same corrections. As both, the incident as the reflective meter, are based on a 18% reflective surface.
Corrections of this kind are the reason I prefer a meter of the kind of the Gossen Profisix, that enables you to "place" deliberately with no effort the metered result at several stops under and above the standard. (Caution: the Mastersix, though having the same scale does not enable this.)