Scythiak Usurpation vs. Ultramarines, Iron Warriors progress, Massilla campaign prelude

Sonofsonsoftaurus and I played a game at home, his Ultra vs. my Chaos Guard, the Scythiak Usurpation.  2000pts, and I had him set up the terrain and scenario.  I am attacking the entrenched Ultramarines, having driven them out of the city (or did I?  Likely a feigned retreat to overextend the heretics) and am trying to break through to their landing areas.  We each get a point for each