Docker Dependency Proxy - Image Prefix

Hi! Noob here using GitLab CI/CD.

My repo is organised like this:

I am working on /mygroup/the-project. First, I develop in my personal fork /gitlabgeek/the-project, then open pull requests to the group level repo.

image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/php:7.4-cli is how the docker container is referenced in .gitlab-ci.yml

When the CI pipeline runs in my personal repo gitlabgeek/the-project, CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX resolves to . Obviously, that failed because /gitlabgeek is not a group, and therefore doesn’t run any proxy. The dependency proxy runs on /mygroup and is confirmed working.

My expectation is that the CI variable should resolve to What did I do wrong?

Thanks in advance!

EDIT: Running GitLab Omnibus 13.12.15, Runner 14.5.1