I have heard of "spitting distance", but not 'sniffing'. As it is, I don't understand the situation well enough to explain how either would be used here. Generally, it means "fairly close".
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People sometimes say things like "I smell victory" when they mean the thing they figuratively smell seems to be almost assured. You also hear "I want it so much I can taste it" and variations on that, meaning that your desire is great.