5.5 clocks: Nearly perfect. Consider this the "perfect" score for most works that do not distinguish themselves above and beyond the call of duty.
So, right now 5.5 clocks is supposed to be considered the perfect score with 6 being something beyond that.
I get the impression that 6 was supposed to be the 11 on the volume knob, and extremely rare. That does not describe most 4 star movies.
The root problem here is that 5.5, with half an empty clock still to go visually, is supposed to stand for perfect. The half an empty clock doesn't look perfect. It looks like it fell short of it by half a clock. When a reviewer wants to give something a "perfect score" they don't want it to LOOK like it was half a clock short of perfect. That's reasonable in my opinion.
The reason Fell wants an explanation for every 6 clock review (correct me if I'm wrong Fell) is because 6 is supposed to be something truly special, something beyond a normal run-of-the-mill perfect score. It's outside the normal continuum.
Making 5 clocks appear with the 6th popping up only in the truly amazing instances is true to the spirit of our rating system. Having an empty clock hanging there on a "perfect" score is misleading and doesn't represent what we're trying to say. It just takes away from the 5's perfectness.