It appears the declipper is not very good at detecting and processing heavily tilted clipping. Even at very extreme settings, there are many false negatives. For reference, this is what I mean:
The two upper channels are input and the two lower channels output.
I can understand detecting these might be a bit trickier (those clips go down below -6 dBFS easily), but considering they are still easily spotted by the eye, I think it could be possible to detect them with an algorithm.
Maybe it already works? If somebody has settings that handle clipping like this, I would love to try them.