I’m pretty sure the actual way of setting values does indeed work correct, but not the reporting of the set value. What you might try is setting a rather large value via API and confirm by testing if that was kept. There’s also the possibility to doublecheck attribute 0x0102 (iirc) of cluter 0xfcc0 if the values sticks or not.
Getting my own in 1-2 days to correct the current value reporting…