[@Kho], When Xos sundered the Celestial Citadel, it was split into two. Half of it fell to the ground, and was rebuilt as the Terrestrial Citadel. The other half, the gem-clad spire and uppermost floors, kept flying, although was in significant disrepair. Xos remained in the flying part, and has not set foot in the Terrestrial Citadel to my knowledge. As such, the fight between Xos and Vestec happened somewhere in the stratosphere.