Top: radial galaxy density profiles of filaments by bins of filament length for the reference catalogue (TNG300-1). The black curve corresponds to the average of all the filaments, regardless of their length, as presented in Sect. 4.1. The coloured curves correspond to the average of length-selected filaments. The gray horizontal line represents the background galaxy density of the simulation box. Bottom: deviation from the mean D_{subset − tot} of the length-selected profiles (see definition in Eq. (2)).