What makes you certain that these values aren't actually physical representations of gas transport time?
Here is an example, where an observable delay between pulse width and WB response, matches the table value for transport delay pretty well:
O2 Response3.jpg
The length of the period drawn here is 0.43 seconds, and the table value is 0.39
I'm still curious about your thoughts on this:
I also don't agree that the "speed" at which the signal crosses stoich (ie the slope), is what drives STFTs to higher values.
I have spent a lot of time looking at O2 sensor response very closely, and see this characteristic a lot:
slopes.jpg
The WB signal almost always rises faster than it falls. Not sure if this is purely a characteristic of the sensor itself, or something about the chemistry/flow of combustion.
I do agree that the slope of the wideband signal is used heavily, but I think it is put through a PID controller. If it makes a correction to a STFT, and after the transport delay has elapsed no change to the WB signal slope is observed, it pushes further in that direction.
Maybe instead of "Transport Delay Time Constant" being some sort of sensor characteristic, it and "Transport Delay" are just the same table, but one for the lean:rich swing, and the other for rich:lean. Just a thought.