SCALE BEFORE TREND
A lapel belongs to a larger composition: shoulder width, chest, collar, shirt and head. Its width should be judged against that whole field, not against a trend photograph in isolation.
Too narrow and the chest can look larger than intended. Too broad and the lapel can consume the front. Authority is not simply width; it is width in proportion.
DIRECTION
A notch creates a break in the line. A peak continues upward and outward. A shawl rolls without an angular interruption. Each gives the eye a different route through the upper body.
THE QUIET TEST
Stand back from the mirror. If the lapel is the only thing you see, the decision may be louder than the wearer. If the face, shoulder and jacket register as one controlled image, the scale is doing its work.