UCC28780: TL431 Rbias affecting the regulation output voltage

Hello,

I'm working on a Flyback active clamp using the UCC28780 controller, TL431 and FODFODM8801AV Optocoupler.

My output voltage should be 22V. The calculation excel file provided by Texas recommand to use 14 kohms in  Rbias resistor (R34 in the schematic)  but with this value i have 19V at the output. When i reduce the bias resistor to 1 kohms i get my 22V but at startup i have a lack of regulation and i have to consume 0.2W so that the voltage become stable. i don't see why changing the Rbias change the output voltage ? do you have any idea of what i'm doing wrong ?

Thank you for your help !