If you want to get me going, show me a "set". When sets are designed poorly there are obvious clues, and they give the set away to the trained eye. And even though these days prettywell anything goes in architecture, it doesn't allways fly, especially if the set is dated in any way.
Bad headers bother me like that. We need them for shootoffs and for ceiling panel suport. When designed well, they are believable as part of the building architecture, as beams and girders are.
What makes a header more believable? Definitely at least a thickness of 8", pref 10". Chamfered edges sell poured conc. very well. Porportions are another factor.
There are two types of header. Shootoff headers are deep, allowing lighting access from an open ceiling. These also are often accompanied by pilasters, which really help sell the architecture, plus they allow easy wilding. Too many pilasters and headers are tricky aswell. When this occurs, I've found subtle depth in the pilasters to work best.
The other type is the support header for the set with ceiling flats and suspended lighting fixtures. In a typical architectural design with divided ceiling panels, the headers would only be slight. The meat is above the ceiling. These would be maybe 8"wx 4" deep, with moulding surround.
Both are picked from the grid by the grip department.
What you really dont want is some wild combination of both. If in doubt, find a good photo reference to follow.