Deep Research Prompting - System Prompt?

Does sonar-deep-research only use the user prompt for queries? I’ve tried to use the system prompt to adjust tone/structure but it doesn’t seem to change anything. If not, what is the best practice for the user query? Is performance reduced with prompt length, or would it have to be significant length to make a difference?

One example is qualifying the type of information to include. For most LLMs, I would use a “DO” and “DON’T” include list in a system prompt. With a deep research system only leveraging the user prompt, it might work better to outline the information that I am looking for and add a post-processing step to remove the information I don’t want.