Mirrored Rearguard Battle - Reinforcements not mirrored

[3Form]

Hi again, just trying my hand at some rearguard battles and set up a mirrored match (as that seems to make the most sense). First wave of reinforcements have arrived in both games, unfortunately (for me) they are vastly different. Is this working as designed as I would expect them to perhaps be also mirrored?

[rbodleyscott]

The mirroring only mirrors the map, not reinforcements.