  The present work continues our previous studies of pom-pom molecule [K.
Haydukivska, O. Kalyuzhnyi, V. Blavatska, and J. Ilnytskyi, J. Mol. Liq. 328,
115456 (2021); Condens. Matter Phys. 25, 23302 (2022)]. The molecule consists
of a linear backbone with two branching points at both ends, with
functionalities $f_1$ and $f_2$. Here, the main attention is concentrated on
studying the impact of the central backbone length on the configurational
characteristics of complex molecule, such as size and shape ratios. We apply
both a direct polymer renormalization scheme based on continuous chain model
and the alternative Wei's method to analyze a set of size and shape properties
of pom-pom polymers in dilute solution. The size ratio of a pom-pom and a chain
polymer of the same total molecular mass is calculated with an excluded volume
interaction taken into account, and estimates for asphericity are found in
Gaussian approximation, whereas for the size ratio we found a monotonous
dependence of the length of backbone at different functionalities of side arms.
Results for asphericity show a non-trivial behaviour.
