Analyzing emotional depth in custom backstories versus system prompts

Hey everyone. I have been running some tests lately trying to figure out how background lore affects long term memory and conversational tone in companion apps. Specifically I am trying to understand if a dense narrative backstory produces better emotional consistency than keeping the instructions strictly inside the system prompt area. Sometimes my companion starts drifting into generic assistant mode if the backstory gets too cluttered with worldbuilding details instead of relational cues. I am curious how you all structure your characters. Do you prefer writing deep lore or do you focus strictly on behavioral rules? Have you noticed any specific formatting tricks that prevent the AI from forgetting core personality traits after a few dozen messages? I want to hear what approaches work best for maintaining a steady sense of identity over time.