The other question I had is how many points are awarded for this particular event, especially if this is a one-time event - ie. a customer signs up for the rewards program.
If the “Joins Smile.io Rewards Program” trigger occurs once and pending on the number of points awarded for that action you will most likely see most people enter and exit this flow without enough points for any of your emails.
If this event triggers every time a purchase is made as more points are earned, then I think the set up you have will work as expected (As long as you don’t have any filters for the number of times someone can enter the flow).
Otherwise, if there are other events associated to the integration, such as something to placing an order, that might work better for this setup because orders will likely be reoccurring so each time the customer would be entered into this flow and then based on their point totals at that time, they would receive the correct email.