Although they concluded that the for the lowest altitudes ( where I/F peaks) spherical particles fit better and for the rest aggregates fit better than spherical particles, there is still a problem. They assumed that the aggregates have a contstant fractal number, which is equal to 2. It is not realistic to assume a sudden change from fractal particles to the spherical particles near the lowest haze layer. One possible scenario is a gradual increase in the fractal number of haze particles reaching near 3 near the surface. In another words, as the aggregates grow they may become increasingly compact becoming spherical . Another possibility, some material condenses over the surface of the aggregate particles. Condenstation may increase towards the surface. Similar mechanism also suggested for Titan's haze particle at the lowest 30 Km of the Titan's atmosphere.
From \citet{Gladstone_2019}
Pluto’s atmosphere is most similar to Titan’s—with the photochem- istry of supervolatile nitrogen and hydrocarbons resulting in a kind of factory for cold haze production