I think it has to do with many factors including how many people are in an area, is that area marked as a heightened security zone, and are there enough relays in the area for Smokey to extend that far...and probably some additional criteria we aren't aware of yet.

I say relays, because if you've seen the Blast Door Map, it notes areas of "heightened Cerberus (aka Smokey) activity" and areas with "high number of Dharmatel relays". I think all of this relates, as the monster clearly has some limitations.

The map also indicates that Smokey spends most of its time in the so-called Dark Territory where the Black Rock was found.

__________________
"The Naked Gun!"

Frank Drebin remembers a lost love.

Frank: It's the same old story. Boy finds girl, boy loses girl, girl finds boy, boy forgets girl, boy remembers girl, girls dies in a tragic blimp accident over the Orange Bowl on New Year's Day.

Jane: Goodyear?

Frank: No, the worst.