As far as I’ve seen in the industry, most people who set up funds for giving to open source pull their numbers on a somewhat arbitrary basis, based on what they think they can get budget approval for. In Indeed’s example, the FOSS Contributor Fund base budget was set by my picking $10,000 as the number I wanted to give back to open source every month, so the budget was set at $120,000 annually. Most of the other funders I talk to also seem to set their budgets by either looking at their strategic goals and estimating spend, or by estimating what they think they can get approved based on the rest of the spend for their department.
One interesting use case I’m aware of is Citus Data giving a 1% equity stake in PostgreSQL. They talk about this in this blog post that explains their thinking.
Yours might be the first in-the-wild example of a company setting their giveback targets based on revenue. It’s an exciting model that I’ve been hoping that we would see emerge. You should write a blog post about it or do a talk to get the word out!
I do know there are other organizations who are thinking about approaching their funding using a per-developer model similar to Sentry’s, I expect we will see more of them when budgets are set later this year.
We should talk sometime, I’d be interested in hearing more about your work.