Unless you think it really is just a singular point in which case any large situation makes the distance restriction meaningless...
Obviously it's an area but ...
> it's a pretty reasonable expectation that all involved officers are included in that area
That doesn't necessarily follow - 2 cops arresting someone whilst 10 are on, say, crowd or traffic control shouldn't include those 10 cops in the LEA because they're not part of the "activity", per se, but supporting actors, no? Same goes for one that wanders away from the arrest - they're no longer an active participant and can't be included in the "activity", surely?
(Now, I agree, the courts might well say "wherever cops are is a LEA" but I don't think they'd get away with it without shenanigans like SCOTUS.)
A cop walking toward them from 20ft away won't shift the locus of the law enforcement activity (unless he's dragging the prisoner, I suppose) and this should be ruled out as infringement - it would be a ridiculous stretch to say "the mere presence of a cop means law enforcement activity is occurring".