I guess it is WBO2 101 that the free O2, and not the raw fuel or lack thereof, that has the reducing effect on the Nernst cell
So in terms of WBO2 readings, a Pseudo DI engine won't be any different than a port injected engine in a the same state of tune.
That brings up another question in my mind... Engines with different trapping efficiencies will show different lambda readings for the same actual "combustion" lambda... so the sensor never reads "combustion" lambda, which is always richer than the sensor reading due to lost mixture or charge air. I understand that AFR by itself is not a tuning tool. It's like EGT, in that it's a guideline for the safe operating limits of the engine.
The way to deal with the variability of mixture from "actual" is just to adjust mixture to peak torque, and go through the entire RPM range, adjusting mixture for peak torque at each RPM point to account for changes in the engine's trapping efficiency with RPM. Obviously this isn't as big a job as it sounds like... tune for a flat AFR curve, then adjust the entire curve up or down in 0.1 or 0.2 increments to see where in the curve the torque goes up or down, then adjust the fuel (and ignition) curves accordingly.
Regarding the high mount injectors...
Typical fuel injectors at 40-50 psi are lousy atomizers. They really just squirt streams of fuel. Mounting conventional injectors high gives the mixture motion in the runner more time to reduce the droplet size and homogenize the charge, resulting in better mixture quality and more consistent cycle to cycle operation.
While EFI meters more precisely than carbs, a well set up carb can delivery a higher quality mixture than a production based port EFI system, in terms of droplet size and mixture homogeneity.
I've read some topics and posts on Speedtalk discussing high pressure port injection--running 200-300 psi fuel pressures with specialized injectors in the intake runners. These achieved better mixture quality due to better atomization and showed a power increase relative to typical 3.5 bar fuel pressure.
Fuel vapor fraction going through the valve is another tradeoff. Fuel vapor displaces MUCH more air than the same mass of liquid fuel, so you want as little fuel vapor as possible going through the valve, BUT you need some amount of fuel vapor in the chamber to ignite the mixture... so the fuel needs to start vaporizing before it goes through the valve.
OTOH, vaporizing fuel drops the temperature of the entire mixture, increasing air density (and reducing velocity), so there's probably a very specific vapor fraction that results in the greatest mass of air in the chamber... BUT that vapor fraction will depend on some other factors and may be different with high mount vs. low mount injectors, due to the differences in interaction time that the fuel and air have before going through the valve.
In light of that, I *think* Psuedo-DI with conventional pressure relies on the high air velocity through the throat/valve, which is of course the highest velocity in the system at any point on the load map, to help atomize the fuel right as it goes into the chamber, avoiding both the big SLURP of conventionally sized injectors, and the mixture quality degradation from high mount injectors that spray longer than the intake valve is open and experience static air in the runner.
Sooo.... tuning fuel delivery is an iffy, finnicky operation.
However, a DEFINITE advantage of Pseudo DI (PDI? PsDI?) is that it doesn't send raw fuel out the exhaust, so it should show improved fuel economy, particularly at low RPM & light loads for engines in high states of tune, relative to conventional port injection. It should also be easier on the catalysts during extended operation at high engine loads because they don't have to deal with as much raw fuel in the exhaust stream.