This paper presents the recent progress in the development of the on-the-fly global variance reduction (OTF-GVR) method for Monte Carlo (MC) shielding calculations. OTF-GVR method provides on-the-fly weight window mesh (WWM) generation along with the particle transport simulation. In the previous study, the solution for the so-called 'long-history' problem, in which particles are unnecessarily over-split, is empirical and not fully effective. In this work, an innovative method using dynamic WWM upper bounds was proposed, which diminishes the over-splitting particles by relaxing the weight-windows upper bounds. This method has been proven effective through applications for several fusion reactors and neutron source facilities, with excellent performances over analogue simulations and variance reduction runs using common GVR methods.