[Dominik]

The mixing is straightforward.

In reference to my "octane maps" you would have to ask if the processor you use has a 94 (97+91)/2 map where the processor can feel "at home". Else your ECM is "thinking" too long (like a chess computer) if it can advance timing to make use of the higher octane.

The knock sensor does the critical work to protect your engine, but the ECU may not calculate fast enough to make use of better fuel by constantly advancing timing and computing A/F ratio accordingly. The processor speed may no be sufficient.

If your engine makes more power from the fuel can be verified on a dyno.
Run pump gas then add 97. Even run straight 97, too.

I left the department years ago and moved to another country. So I cannot quickly ask for new opinions.

IF you hit borderline of the trouble code setting conditions or even drop into backup mode (which I doubt!), using pump gas should reset your ECU.

An example of cautious programming:
The 1992 1.2 OPEL Corsa had two maps (plus one for backup mode). Uphill they sometimes switched into the 91 octane mapping compensating for pinging. Downhill, or on top it took forever to switch back into the 95 mapping.

(That's RON octane rating for Europe, where we even have 100 octane pump gas from SHELL)