In sound, the optimal rendering is usually achieved when the twitter (typically, the front panel of the speaker) is at ear level when seated. The most suitable accessory to do that with Reactor is Legs.
On the other hand, if you are using Gecko, the best is to place your Gecko in the corner of a room (please be careful, you must allow at least a 5cm margin between the woofer and the wall to enable safe excursion). This placement will create a resonance effect in the room for optimal sound dispersion.
Concerning the distance between the Reactors in stereo, allow at least 1 meter of separation so that you can be between them while listening. The sound will be optimal as soon as your listening spot is precisely between the two speakers.