The point is this: the manual add is in the exhale CL just before the head/sensors and there is not a PO2 spike when flying manually. My unit is designed this way and seems to work just fine.

like you said """It make a lot more sense to inject the O2 before the sensors in the head and the VR3.....Gives the gas more time to better mix with the breathing loop gas and has to give a more accurate reading of the inspired gasses.

The other way has the breathing gas pass the sensors giving you a PO2 reading and then you add to the mixture and inhale it, with the elevated PO2. By the time it gets back to the sensors the Po2 has dropped due to part of the O2 being metabilised. The reading is inaccurate and there is a much higher possibility of having an O2 hit."""