Their raps come off flat cause they ain't in circumference
Other artists' rhymes try to be all that, but fall flat — a play on words; since they’re flat, they lack curve (circumference). Another spin on this line, he’s suggesting that these other rappers come off flat because they are not well rounded.
They are not in the circumference (of Lupe’s circle). They are not around Lupe. Lu is saying that other rappers aren’t in his inner circle of rap peers, hence they pose no challenge.
When a tire loses pressure, it has to come off because it is no longer inflated and fully round.
Coming off flat could also mean hitting the wrong tone (typically when public speaking or singing) due to incorrect posture “curve” and breathing.
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