Divine star heals the caster initially and then once again on its return. Is the heal accounting for the caster as a target? Also is development taking into consideration the star hits targets on the way back for heals as well? There is a lot of movement going on at times so if Divine star hits 7 players on its way out, it could be hitting 8 or 5 players on the way back. Please clarify or add more details.
Diminishing Returns for Divine Star are actually calculated on a per-target basis. What that means is, when someone is healed, it checks to see how many other targets were in a close enough range (at cast time) to also be healed, and reduces the amount accordingly. This way, it doesn't actually matter how many other players have been healed already or not -- only the number of other players that are being healed at (roughly) the same time.
So, if someone moves into or out Divine Star's area while it's in motion, any heals that happen as it continues to path will only diminish based on the number of other eligible players that were close to the healed target at cast time.
EDIT: Reworded a couple things, for clarity. Apologies for any extra confusion :)