Bonus to be paid on Basic+DA or Gross - If we consider only Basic+DA most of the employees are eligible for a bonus

Hi Team, This is Lokesh and I'm working as an HR in one of the private companies.
My query is about Bonuses. Bonus to be paid on Basic+DA or Gross. Our company Salary Structure is Basic+DA, HRA, Special allowance, Addl HRA, Other Allowance (All are fixed). If we consider only Basic+DA most of the employees are eligible for a bonus. If we consider Gross Salary only a few employees are eligible for the same.
Please do let me know, What are the components to be taken to pay the bonus.