Calculating Employee Bonuses based on Salary AND Tenure

I am having a major brain cramp in how to calculate Column H in the attached.

What I'm looking to do is create a "fair" allocation of a bonus pool for our company. The idea is to reward employees with an emphasis on their tenure with the company, as they've worked from the ground up, but also keep salaries in mind. Is there a formula-based way to take a bonus pool of money, and divy it up based on time with the company while also factoring in annual salary? I need to include their salaries so that it feels like a true bonus to each individual based on their various individual compensation levels.

Thanks in advance for any advice along the way!