I just happened to be re-reading CuF. On p.162, Amara says, "If Kalarus's forces take Ceres, there will be nothing to stand between them and the capital." And on p.163, Gaius says, "I'm dispatching Third Imperian to your aid, but they cannot reach you before Kalare's forces. The Crown Legion, however, was on maneuvers south of the capital, and I ordered them to your aid within an hour of the attack. They've been force-marching through the night, and Sir Miles should be arriving with his men within hours. . . . I have already asked High Lords Placidus and Atticus to send relief forces to link up with Third Imperian."
Based on the above, I think Alera Imperia should be where Placida is currently positioned in your map. Currently, the map doesn't support Amara's statement since Kalare would have to go through Atticus to get to Alera Imperia, and the Crown Legion maneuvering in the south of the capital would not have a rapid response advantage since it would have to march through Atticus to get to Ceres.
Edited to correct the last statement.