As above

"As above, so below" cannot be a statement of fact because it isn't.

It must then be a principle applied to divine truths only.

It is obvious that the apparent structure of physical reality is not the same as the structure of "heaven". Thus naïvely, a truth in physical reality does not necessarily have to be true in "heaven", and vice versa.

This happens so that those who speak of divine truths are often ("correctly") perceived to be speaking falsehoods, since they are invalid on the physical plane.

As such, when spreading divine truths, one must strive for alignment between the two realities. This is why in multiple traditions the teachings have multi-layered meanings, from parables from Jesus, to the puns of Zen, and then this Hermetic principle -- "as above, so below" must refer to those teachings that are valid both above and below, transcending multiple realities at the same time.