Correctly reading fuel trims on E92 and changing for 'real' gasoline not E10

Its been a while since i've been back here after a number of country changes for my job (over in Europe).

Anyhow, i've been lucky enough to get myself a US spec C7 Z51 Manual and want to really get an understanding of the tune

My intro being said - I cannot find the fuel trim log for an E92 in v7.5 scan
I read elsewhere in this forum to log on to the ECM as a different controller, E38 maybe ? or one of the other SIDI ECMs.
I've searched high and low and cannot find it. Can anyone tell me how to read my fuel trims??

Following on, currently in Germany we have 98+ RON gasoline E5 (max), but many retailers are more or less pure gasoline.
I want to measure the fuel trims now as the E92 has stoick set as 14.11 on the C7, but i'd like to dial it in closer to 14.6 (maybe at 14.55 to account for some Ethanol).
I know about WB sensors and that I need to set my fuel to correctly evaluate AFR, but I'd like to understand how Narrow Bands really work.
Without much deeper thought, i'm sure 450mv is not correct for E10 and pure gas.... maybe the difference is only 10s of mv, but i'd like this dialed in right, so
then I can play with the 'torque response' and see how the car behaves

EDIT - unless I'm having a brain glitch and narrow bands in terms of voltage is just a lambda, and lambda is well lambda and only converts to an AFR for whatever fuel is used. ?? I feel to be going a little bit in logical circles