Astronauts participating in deep-space exploration missions will be exposed to significantly greater amounts of radiation than is typically encountered on Earth or in low Earth orbit (LEO), which poses significant risks to crew health and mission safety. Active magnetic radiation shields based on the Lorentz deflection of charged particles have the potential to reduce astronaut doses with lower mass costs than passive shielding techniques. Typically, active shielding performance is evaluated using high-fidelity Monte Carlo simulations, which are too computationally expensive to evaluate an entire trade space of shield designs. A rapid, semi-analytical model based on the High Charge and Energy Transport code (HZETRN) developed in 2014 provided an alternative method by which to evaluate the performance of solenoidal shields. However, various simplifying assumptions made in the original model have limited its accuracy, and therefore require evaluation and correction. In this work, a number of aspects of the original semi-analytical model are updated and validated by Monte Carlo simulation, then used to recharacterize the design trade space of solenoidal magnetic shields. The updated model predicts improved performance for weaker shields as compared to the original model, but greatly diminished performance for strong shields with bending powers greater than 20 T-m. Overall, the results indicate that magnetic shields enable significant mass savings over passive shields for mission scenarios where the requisite dose reduction is greater than about 60% relative to free space, which includes most exploration missions longer than one year with significant time spent outside LEO.