Tomcat AJP vulnerability CVE-2020-1938 aka Ghostcat

I have a question about Tomcat vulnerability CVE-2020-1938 aka Ghostcat. The security researcher who discovered the vulnerability created a write up here: https://www.chaitin.cn/en/ghostcat and a PoC here: https://github.com/YDHCUI/CNVD-2020-10487-Tomcat-Ajp-lfi.

Can this vulnerability still be exploited when Apache is acting as the reverse proxy for Tomcat (and communicating with it using AJP) or would it only work when communicating directly to the AJP service on Tomcat?

I can’t get the POC to work when using Apache as a proxy but I don’t know if that’s because of my lack of experience with Apache, Tomcat, and AJP and/or the lack of implementation in the POC to support exploitation over such a setup OR if the vulnerability is in fact only exploitable when communicating directly with the AJP service port 8009 on Tomcat.