@IntegRa
if it can helsp, please find here below my specific XU4 setting to have XU4 fan running all the time according a smooth "curve".
May be possible to adjuted depending on your fan builtin quality.
Settingof S02fan :
0_1574527848120_2019-11-23-FAN-XU4.PNG

Graph :
0_1574527869579_2019-11-23-FAN-XU4-GP.PNG