My design is supposed to have a 17 V Output. Measured Output Voltage of the prototype was 14.6 V.
Consequently I entered this value in PIXIs Designer 9 in  "Measured Output Value". The proposal for RLOWER_FINE was 6,5 KOhm instead of 5,5 KOhms accordingly. I adjusted the lower resistor and the result was an even lower output voltage of 11 V. The Decrease of the lower resistor to 4,7 KOhm lead a higher output voltage of 15.5 V, which were a bit more unstable than the 14.6 V before.
How come PIXIs Designer suggests a higher resistor which makes output-value become worse?