Note that Geany does in fact detect the prefixes you suggested:
Yes, but it only works for existing files. If file is not saved, Geany doesn't detect any of prefixes, and the only way to get syntax highlighting to work is to:
1. Manually save file; 2. Manually set file type using your previous suggestion (_menu->Document->Set Filetype->Scripting Languages->PHP Source File_)
See what I mean - https://i.postimg.cc/MHh2RNhQ/geany.png
As you see, file is not saved yet, so Geany doesn't detect PHP filetype for some reason.