Good news for today!
I purchased the ethanol map pack and flashed my car with the E30 and filled my tank with E30 blend.
The car feels much stronger, and I clocked it at 396 hp DIN corrected under the actual weather conditions, using measured weight of the car...
I still don't know why it was so weak on 98RON, and even 102 RON, but I'll try again later. I'm now quite satisfied with those perfs, at least until a bigger turbo comes in the game