Trying out multi quoting so bear with me...
If you put it miles away from anything else, you are likely looking at having to roll a 6+ for a D3 MW output to units around a single piece of terrain. Keep in mind you have to throw a Priest or Oracle inside to zap stuff - This means not only are you likely doing no MW output, you will also have an important support hero with an important buff miles away from anywhere else. Certainly not worth it IMO. The opponent can also simply choose to go attack it with a flanking unit - A Skink Priest wont survive much even if he get +1 save and -1 to be hit.
Fair enough, tbh it's hard to speculate distances though. It might be better in this situation instead of placing it in the far corner of deployment place it in the middle of a deployment zone? Keep us in range for things like bastiladons near enough to get a benefit from a skink star priest, while still giving them, and the terrain piece range. Remember that in this scenario we are facing an army that wants to move towards us, so the ranges get even smaller than just measuring the board.
As far as the opponent getting it in this situation, they still would need to hold back a unit, all be it to a lesser extent. If they completely ignore it, and we're star borne maybe this gives us a better reason for oracle on trogladon with LoST? If not then we potentially lose out on anything for the piece. Worst case, we cant shoot a high priority target for a turn, maybe two. Medium case, we cant use it all. Best case the oppoent choose to play and position in a poor manner, hoping to get their 'buff'.
The piece has to be wholly within your territory to garrision it upon deploying your unit. Otherwise your unit must be within 6" and use your movement to garrison it. I dont think you can put it square in the middle and still be within 6" at the start of your 2nd movement phase.
Keep in mind the units inside suddenly got a 6x6" hitbox too, so the surface area is suddenly huge - Your support guy is now much easier to surround and kill despite getting +1 save and -1 to be hit. Unless you plan to throw Bastiladons inside. Also keep in mind that if your opponent runs up and is within 3" of the terrain piece, he has denied you from garrisoning it.
Note this option was still assuming it was in our deployment zone, either fully or partially. To guarantee we can get in auto, or turn 1 movement. The idea is that we would send our front line troops up creating a screen for our temple and wizard. Also granting look out sir. Thus eliminating the fear of being surrounded and killed.
The position should eliminate any enemy unit nearby denial.
Note if the enemy picks it, this could also potentially limit thier front line advance, either limit some units to a 6" move (if the had more) or forcing them to deploy around it and circle it ( at least a bit ) to get closer to us.
The whole purpose of the terrain piece for me was to zap support heroes etc. near terrain. That couple with Comet's Call from my Kroak could put some damage into the opponent's support heroes. Now if you have to put the terrain piece almost dead center, you simply risk your dudes getting killed. As mentioned before, the terrain is like 6x6", so it is very easy for the opponent to charge and surround the terrain and kill whatever is inside. +1 save and -1 to be hit is good, but it doesnt make whatever is inside immortal. I would much rather have my Skink Priest sat behind a screen or two, than get charged while inside the terrain piece.
I think this more an issue of adapting to a different strategy. For its obvious use of zapping people with MW, this strategy is useless I agree, In this option, it is being used more as a fieldable LOS and movement impediment. The idea would not be to garrison it with our units, merely bait an interaction at an objective. If the opponent comes in we'll hopefully have set ourselves in a more advantageous position then them.
If they don't then maybe we garrison it to hold the object more secure.
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Again these were just off the cuff spitball, for someone who hasn't played any 2k games, and only a hand full of 1k ones.
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Just to be clear I really appreciate your input, you definitely have valid points and made me push my brain for some responses. Thanks for the excellent constructive criticism!