I know this, but I'm assuming the dive in the AFR is because of fuel being added too late to a a hot mixture on its way out and burns up some of that air.

Indeed, but if you're spraying right up to ignition, the end of spray won't have had time to homogenize so will end up in the exhaust manifold along with unburnt oxygen from other charges. This is only my theory, but it's based on observations from my own car and seems to correspond with my big orange book of GDI. I agree that EGT could be a concern here, but I've not got a probe and hybrid I'm running just now is considered "disposable". I use the car as a practical learning platform. Omelettes and cracking eggs etc.