This article should answer your question. Only missing from the list is 11 stars reserved for high legend players.
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Q: How many stars bonuses do I get at the start of the season?
A: It depends on your current MMR and the rank you reached from your previous season, whichever gives a higher value. Generally, the minimal initial star bonuses you get for each rank floor you reached are:
Minimal Initial Star Bonuses
Thank you, but it doesn’t actually answer the question, since the table doesn’t account for in-between ranks. I reached legend last month, but don’t feel like grinding again. If it’s MMR-based, then I guess it should remain the same. Yet I’d love to hear from the people who finished D4-D1 last month.