The best placement for Galaxea is nowhere near my tank... haha
But to actually answer your question, the key to galaxea as I'm told is to get the flow right You want to have the flow pushing the stinging tentacles away from its neighbors, otherwise you can't put anything near it. I've heard some people like right under a powerhead, I've also heard near the glass with the flow pushing towards the glass (as opposed to toward the rock structure and other corals). Othereisw it's a pretty hardy coral to my understanding. Just plan for some potential growth too