I don't word directly for F5 bt everyone from F5 will tell you to use ASM on the same F5 device if there is enough CPU and memory. There can't be a guide for how F5 APM will work with concurrent vendor, as there as many waf vendors nowadays as there are stars in the sky 🙂
As I understand you want to use Sophos in L3 mode, right?
You can search (google) for F5 reference architectures. You will find a couple of diagrams that actually recommend to have a L3/4 network firewall, like F5 AFM, in a separate tier in front of APM or ASM/AWAF, in order to protect from flooding attacks for example.
This link is a bit dated, but is close to your scenario: The F5 DDoS Reference Architecture - Enterprise Edition.