The concept sounds good.
This alternative too, if it's not too much, of course:
1st star: 25% of salary as merch
2nd star: 20% of salary as merch
3rd star: 15% of salary
And so on and so forth.
If you add 10% to the 4th top player and 5% to the 5th one, you'd have a medium 15% for your "supposedly" starting five or, at least, 15% of your 5 top players, which should be around half the whole squad.