The edge of a shadow starts with source size
More output does not soften a nose shadow. Read the size of the emitting surface as the face sees it.
Illumination and shadow edges
A small torch creates a distinct boundary between light and shade. A broad window can produce an extended transition because different parts of the source remain visible around an obstruction. Increasing light output and enlarging the emitting surface do different jobs.
The emitting surface seen from the face
Calculate angular size from your inputs independently of the photograph. This assumes a flat source facing the subject and does not predict exposure or relight skin.
A 90 cm softbox is not one fixed light
The same surface looks larger at 1 m than at 3 m. A smaller nearby source may appear larger than a bigger distant one. Rebalance exposure after moving the light so that an increase in brightness is not mistaken for softer shadow edges. The model below calculates angular size; it does not relight skin.
Check the lit surface, not just the diffuser
A small translucent cap may spread rays without becoming a sufficiently large source from the subject’s position. A large diffusion frame also needs to be illuminated across its surface. A bright center inside a mostly unlit frame does not behave like the entire frame is emitting evenly.