Thank you for your response. I simulated the molded part using the average melt temperature and the average mold temperature: PP (230°C/35°C) and PS (225°C/40°C). The results are as shown above. It is possible that variations in temperature lead to differing outcomes and conclusions.

I appreciate your clarification, nonetheless.

I have simulated the flow myself, and found that the flow results for the two materials in the upper figure may have been reversed, as shown below:

Melt Front Time results about PP and PS