Different forms of the NG function h(r) versus (vs.) heliocentric distance r (Eqs. (3)–(5)) investigated in this paper. Standard g(r) is shown with a black curve, and a Yabushita function f(r) with a dotted blue (dark grey) one. From top to bottom, according to description given in the figure: dashed green/grey (m =  −2.15, r₀ = 4.0), solid cyan/grey (m =  −1.9, r₀ = 4.0), and dotted-dashed cyan/grey (m =  −2.15, r₀ = 1.5) curves represent the best derived g(r)-like functions for the comets C/2001 Q4 and C/2002 T7 for three types of data (ALL, PRE, and DIST, see Sect. 3.1).