The fuel pressure at 3.6 bar sounds good.
Do you still have the P0170 trouble code ?
Did you also check the function of the fuel pressure regulator ?
Have you measured the pulse width on the fuel injectors with your picoscope ?
The LTFT affects the basic fuel duration of injectors and when the LTFT are negative it subtract x number of milliseconds from the base injection width.
You should look at areas that make the engine runs on a rich mixture.