Two text generation systems are configured as follows. System A: nucleus sampling (top-p=0.95), temperature=1.0. System B: nucleus sampling (top-p=0.5), temperature=1.0. Both use the same LLM. A creative writing application evaluates both. System B produces more focused, coherent narratives but less surprising plot developments. System A produces more unexpected turns but occasionally goes off-topic. Explain the precise mechanism causing these differences.