Ok, I got a little sloppy there. Technically it's the converse of Poe's Law. Although the converse is not logically equivalent to the direct statement in all cases, it is in the case of T => T, which is the usual. Thus, informally, Poe's Law is sometimes invoked in the converse as well.

Poe's Law says any extremist writing, sufficiently well-written, is indistinguishable from satire.

The converse (interchanging precedent and consequent and keeping the "sufficiently well written" clause in place) would be something like this:

Any satire, sufficiently well-written, is indistinguishable from extremist writing.

T=>T would be:

Satire is sufficiently well written (T)

Satire is indistinguishable from extremism (T)

Both are true so the statement is true even if precedent and consequent are reversed.

Ok now?