How did the levitating platform work?

Question

In chapter 35 of Words of Radiance, Navani oversees the experiments around a levitating platform.

The experiment actually involves two wooden platforms (A and B), each having a set of stormlight infused gems. It is explained that the gems in A are linked to the gems in B (and viceversa), since they are halves of the same stone.

I'll give a brief summary of the experiment, but I don't have the book at hand right now (I may be editing this later to be more accurate):

Image reference.

1. Platform A is set upon a moving wooden structure on wheels, so that it stays elevated from the ground. A is also connected to a set of ropes and pulleys, but those don't serve the purpose of keeping it up.
2. Platform B (the tower) is laid out on the ground. On its surface there are mannequins, resembling soldiers.
3. The moving structure on which platform A lies is slowly neared to B's location, until they are few meters (?) apart.
4. The moving structure gets slowly removed from under platform A, which stays in place mid-air.
5. Ardents start pulling on the ropes and lowering platform A from its midair position. This causes platform B to rise, effectively floating.
6. At the end of the experiment, A is on the ground, while B is floating at A previous height (see points 1-4).

Navani explains that since the gems in the platforms are each half of the other, the platform are "connected in tandem". I don't recall correctly much of the explanation (again, I may come back to edit this later).

If we accept that platform B rises because A is taked down (since they are linked), why didn't platform B move when A was brought near?

In other words, I don't get why vertical movement affects both platforms, while horizontal movement can affect one (in my summary, platform A) and not the other.

Answer 1

The fabrials connecting the two platforms weren't activated until after the platforms were put into place. When we switch to Navani's viewpoint, both platforms are already in place, so we don't really see them being transported there. When they begin the experiment, we get this sentence:

Ardents at the top had activated the fabrials there, and now climbed down the ladders at the sides, unhooking latches as they went.

Unless they were on the platform the entire time while it got carried there, this means they only just activated the fabrials shortly before the experiment began. In particular, there was never any relative horizontal movement while the fabrials were active.