What you can do is place your spikes half-way between the ceiling and the floor, then set the sine's magnitude to half the distance between the ceiling and the floor.
If that distance varies, you'll have to compute it somehow at the start of the layout or when the spike is created.
In the sine behavior, set the movement to vertical and your period offset to :
- 0 if you want the spikes to start at the middle.
- quarter of your period if you want them to start at the floor
- minus quarter of your period if you want them to start at the ceiling