Car stick shifts vs. bike front-derailleur operation
We thankfully have a standard for driving automobiles. We can operate a new or a rental car without reading its owner's manual. Reading the manual is useful for many basic details, but the steering wheel, braking, and, especially, shifting are universal.
When bikes do come with an "owner's manual", the manual is written by lawyers ("do not operate without a helmet") and addresses neither basic maintenance nor even operation. It's necessary to search for the actual documents online. The details of operating front derailleurs in conjunction with rear derailleurs have subtleties that make riding a new bike inherently iterative to avoid all chain-cage rubbing.
2x Front derailleurs and the mysterious third middle position
Many 2x (road bike) front-shifter-and-front-derailleur sets have three settings.
The derailleur-cage-at-its-leftmost setting is used for, vaguely, the 50% of larger-cogs rear-derailleur settings. Those are positions I and III in the illustration (although the large-chainring-largest-cog is unlikely to be usable; the chain will most likely rub on the front derailleur cage).
The derailleur-cage-at-its-rightmost setting is likewise used, again roughly, for the 50% of smaller-cogs rear-derailleur settings. Those are illustrated in II and IV in the figure (the smaller-smallest chainring-to-cog is likewise generally unusable).
Is there a standard for knowing whether the middle of the front-derailleur shifter is to be used for II only, for III only, or for both II and III?
In other words, when you start riding an unfamiliar bike, do you have to search for its Operator Manual (online, probably) to learn how to shift properly?
Indexed shifting (which is now so widespread it may have completely pushed friction shifting out of the new-bike market for years) greatly helps with the leftmost and rightmost cage positions. The shifting interface consists of a clean click. Each click lands on a precise setting.
If we access the middle position from the large-chainring, we cleanly drop to an indexed position, but I haven't been able to determine whether accessing the middle position from the small-chainring (pulling the cable more taut and lifting the derailleur cage halfway) will always pull the cage also to an indexed position. Does it?