What is the plane of imported traces?
When traces are first imported into a block, the PCB (block) is considered to be in the XY plane - which implies the layers are stacked in the Z-direction.
The bottom layer is at Min Z (Z= 0) and the top layer is at Max Z side of the board.
After importing the trace layer, the block can be moved and rotated.
The trace layers will follow the board with any such operations.
For additional information, refer following section:
Icepak 12.1 User Guide -> Importing and Exporting Model Files -> Importing Trace Files into ANSYS Icepak -> Importing Trace Files