Let's assume that you've already asked permission to draft, etc etc because otherwise @
rubiksoval will be unhappy. According to
https://www.cyclingweekly.com/news/p...rafting-349941, the benefit to you has a pretty good range, up to 20m (assuming no wind). So basically choose whatever distance you want.
The flip side to this--the same source
https://www.cyclingweekly.com/news/l...w-study-458203 says that drafting is probably not a great idea right now.
Take your pick?