Let's start with the capital letters.
Bearing for Roman is relatively simple, or at least in theory it is based on clear principles.
The LSB and RSB in /O/ are the same; the LSB for /D/, /E/, /F/, /H/, /I/ etc are the same, and so on.
In Italic, on the other hand, I see completely different settings in various fonts. In GaramondPremierPro the measurements are completely different even for the same rods; in the Palatine the LSB is the same for /H/ and /I/, but completely different between /E/ and /F/, which nevertheless have the same design.
What then is the logic, the general conceptual approach of bearing, precisely for italic?