To be fair I have seen false alarms from the sun on glass coffee tables, mirrors on walls, pictures on walls, and this has been regardless of where the detector is facing. Id agree that Fa's the same time everyday is most likely sun this time of year, but I would be surprised if it was direct through the door.
Its unusual for the sun to go directly into a detector through a window the sun is usually higher than the window and beaming down not up. Many of the detectors in my offices are facing the window and they are standard honeywell pir not even quad, (they were here when we moved in we just replaced the panel) and we have never a problem with them. You could say thats because we are open everyday, but not weekends bank holidays, we were even closed for a whole week during the pandemic and we never had a FA.
Im not saying it cant happen and I respect your opinion SWB, I think its rare and although you saying a quad is a workaround, I say its technology designed not to FA when the sun reflects into it.
Having a detector opposite a window also provides a visual deterrent to anyone looking in