I tried to create some custom compositions and realised that both Zeus and 3den ignore the Z value of an object's position. Therefore, only compositions which do not use the third coordinate are currently possible.
Exampel:
class Object38{side=8;vehicle="Land_BagFence_Short_F";rank="";position[]={-6.73193,-3.28879,1.42262};dir=274;};
Even though the height is 1.42262, the sandbag will be created at 0 meters.
I can send the mod via PM to a dev if reproduction is necessary.