First you address the critical factors, then extend your attention to other contributing factors. In the abstract it means adding boxes and arrows to the flowchart to reflect the added logic. In practice it means expanding the GIS macro code, and most importantly wrestling with the model's calibration. For example, it's easy to add a fourth row to the landslide flowchart, identifying the additional criterion of depth to bedrock, and tie it to the other three factors. The previous discussions focused on the hazard of landslides, but not their risk.
Risk implies the threat a hazard imposes on something valuable.
Common sense suggests that a landslide hazard distant from important features represents a much smaller threat than a similar hazard adjacent to a major road or school. Figure 1 shows a risk extension to the rating model that considers proximity to important features as a risk indicator. Increasing map values indicate locations farther from a road. The logic in that refinement is that in steep areas the buffer width increases as a landslide poses a greater threat. The threat diminishes in gently slope d areas, so the buffer width contracts.