I can’t claim credit for it - it was
@Killer Angel who had the idea!
To cite myself, I've thought of (basically) 3 options to place the RE
Realmshaper Engine - placement tips
not something you can optimize, but it’s useful to know how you can employ our terrain, given that the rules for its placement are awful.
first problematic rule: any Realmshaper Engine must be set before any other terrain features are set up, more than 6" from any objectives and more than 6" from the edge of the battlefield.
second problematic rule: you must garrison the terrain with a seraphon wizard or priest if you want to use its effect.
third problematic rule: the RE can be garrisoned also by enemy unit (Garrison rule:
a unit can be set up as a garrison at the start of a battle if the terrain feature is wholly within the unit’s territory. Alternatively, a unit can garrison a terrain feature instead of making a normal move if all of its models are within 6" of the terrain feature, and there are no enemy models within 3" of the terrain feature or already garrisoning it. this also means that you cannot LoSaT into it)
fourth problematic rule (as per latest FAQ): a wizard on Balewind Vortex cannot stay in the RE, it’s removed from the garrison and placed at 1” from it.
Of course, the BIG problem is that, when you place the RE, you don’t know if it will end in your territory or in the opponent’s… with the latter option, not only you are not using it, but you are gifting your opponent a solid base that can be garrisoned and blocks your LoS. This sucks to the point that many players simply don’t bring the RE to the table, even if it comes for free in matched play.
However, there are some tricks that you can use to place your RE in a way that will let you gain advantages. Let’s see.
first option: if you play with the official scenery deployment rule for matched play printed in the GHB2019 (You really should), each player chooses a number of terrains (which are divided into primary and secondary ones). The terrains that got a warscroll have the abilities listed on the warscroll; pick Arcane Ruins as one of your primary terrain, as Arcane Ruins come with the arcane rule (+1 to cast and dispel)
Setup the RE and the Arcane Ruins on opposite deployment zones, forcing your opponent to let you garrison the Realmshape or to concede you a further +1 to cast / dispel. It’s a win-win.
second option:
It’s the simplest. The RE must be placed at more than 6" from obj, so it's useless to control them. Place it in a place where it gives no additional benefit at all (for example, units placed behind it to negate LoS won't control obj)… in this way, if it ends in the enemy territory, your opponent simply won't gain any kind of tangible benefit from it.
Basically: 50% good, 50% nothing happens.
third option:
Requires some planning. Place the RE in a useful place, that could be annoying for you if garrisoned by the opponent. If the RE doesn’t end in your territory, it will act as a bait… and you will make the enemy regret the choice of garrisoning it. You just need to have a list ready to exploit the trap.
Examples: that huge piece of terrain is a great target for spells as Aethervoid Pendulum and every spell that deal those sweet MWs that ignore the +1 to save granted by the garrison (think about Kroak and a triple celestial deliverance).
Or Place the terrain at the outer limit of a territory. If it ends in the enemy's, set up your terradons at the minimum distance from it (usually 24"), buff the terradons with something as priest and starpriest and drown the garrisoned unit with MWs.