According to Islamic Finance, all Investors are liable to earn the same returns, but the projects show variable returns. How do you justify that?

Returns in Islamic Finance

In a Mudarabah or Musharakah contract, all investors are represented as one unit in the contract. However, some investors (Lead Investors) get 1% higher returns as Hiba (Gift) from the Project Developer to encourage and thank investors who are willing to put a larger amount of investment in the project.