<p>Understanding the extensional rheology of viscoelastic fluids is fundamental to advancing a wide array of modern technologies, from precision inkjet printing and high-speed spraying to the controlled formation of droplets in microfluidic devices. In this study, we employ the dripping-onto-substrate capillary breakup extensional rheometry (DoS-CaBER) technique to investigate the capillary thinning dynamics of polymer solutions composed of varying ratios of Newtonian and viscoelastic components. By applying a physically grounded modeling approach, we develop an automated method to identify the transition point between the visco-capillary and elasto-capillary regimes, enabling robust extraction of key rheological parameters. Our results show that increasing the glycerine content leads to higher extensional viscosity, longer relaxation times, and an extended elasto-capillary regime, reflecting enhanced viscous drag and polymer entanglement. Notably, the extensional viscosity in the visco-capillary regime approaches the Newtonian Trouton ratio as the solvent fraction increases, indicating a shift toward solvent-dominated flow behavior. These findings provide new insights into the interplay between viscous and elastic forces in capillary thinning and offer practical guidance for the design and control of extensional flow processes in complex fluids.</p> Graphical abstract <p></p>