I don’t know the equation they use but I can tell you if that person visits every day you’ll never get the full coin amount from them. You’ll get day 1 footfall every day. If they skip a day, you’ll get day 2 footfall. They have to not visit for those 5 days for their next visit to give you the full amount.
Note: This is further affected by this:
So the more traffic you have in total, will also cut some coins off the top.