I am very curious to read the responses. I raced criteriums 30 years ago. My formal rule of thumb was never be further back than the top 25%. Otherwise your risk of crash goes up exponentially, and you are working very hard with the constant accelerations to stay with the pack. When you ride closer to the front, you generally ride a lot smoother

Edit: Watched the video. Those little merge curbs in the round about turns are gonna suck. Those cut the width of the road in half. "Hold your line!"