Just guessing here. The new system might be like:

09-10 stars: 3 purple medals, 50% chance
10-11 stars: 4 purple medals, 40% chance
11-12 stars: 5 purple medals, 30% chance
12-13 stars: 6 purple medals, 20% chance
13-14 stars, 8 purple medals, 15% chance
14-15 stars, 10 purple medals, 10% chance
15-16 stars, 12 purple medals, 10% chance
16-17 stars, 13 purple medals, 10% chance
17-18 stars, 15 purple medals, 10% chance