As I posted earlier, it may just be a minor tolerance difference.
IMO the better clip indicators actually track the path losing negative feedback so differences between voltage clipping would be minimal, but even this more accurate monitoring the loss of feedback will be triggered before voltage clipping by current limiting that could use 5% tolerance parts (or worse from device varaince).
If they indicate the same for no load, but differ under load, current limiting variance could be the reason.
JR
PS: Note slow clip indication is an old (dirty) trick used to make amplifiers appear more powerful than they are, because customers are not very sensitive to small amounts of clipping.