A couple of items to think about, things I have run across in my career:
Some companies I have worked for believed that if you worked the full plan year without performance issues and the company paid out a bonus for that plan year, you would receive the bonus even if you left the business after January 1. This was not based on entitlement, but rather the core set of values on how we wanted employees to be treated, and our desire to build trust with the employees as a management team. A bit of practicality to note, a new company will either buy out the bonus or wait it out. These included management bonuses as well as sales bonuses - all based on annual results.
Other companies took another approach and felt that the bonus was not earned, regardless of audited results or performance of the individual, unless the individual was employed at the time of payment. This brought a few court challenges - allegedly the company moved the payment date to avoid paying to an individual it knew was leaving, and that allegedly the performance period was the plan year, not this "arbitrarily" defined period of when payment was made. The perception of employees was this was being "cheap".
To offset the challenge on these, one company chose to define the bonus (sales) as both selling and servicing the sales after the period had concluded and set up a defined period in which payments would be made.
All in, I guess you have to evaluate the employment "Brand", the principles the bonus is built on, taxation and the company values. In my opinion, carefully evaluating alignment with Brand and values while balancing the financial aspects is going to give you the best, defensible result with employees and management.