Polbius says three feet all around, so the pike goes to your right and you then have three feet clearence behind just to make sure you don't scewer the guy in back.
That doesn't preclude pushing with pike though, the difference would be that the push would be more from the threat of been scewer by five pikes, rather than by weight of men. Which effectively means five ranks are as effective as sixteen, though the latter allows you depth, angled pikes to protect against missiles and a less vulnerable flank.
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