With continuing increase in soft error rates, its foreseeable that multiple faults will eventually need to be considered when modeling circuit sensitivity and evaluating fault-tolerance techniques. Previous work that considers multiple faults assumes the faults are permanent. These assumptions aren't directly valid for soft errors. In this work, we evaluate two currently available models for analyzing circuit sensitivities but subject them to multiple transient fault environments. The first model targets the application of triple modular redundancy (TMR) to a non-branching (no fan-out) circuit with permanent faults. We demonstrate this model's inability to adequately predict sensitivity when circuits with branching are considered and subjected to transient faults. We motivate the need for a model that captures logical masking. This is provided by modifying a soft error rate (SER) estimation algorithm to handle multiple faults and gate input interdependence. We conclude that the simple non-branching model can predict a trade-off threshold for when TMR can benefit a circuit. However accurately predicting the magnitude of reliability changes requires the inclusion of more complicated branching effects and logical masking.