So you basically inputted some elements from both Halo: Reach and The Fall of Reach together into this comic? Because if I recall the plot descriptions on the Halo wikipedias, there wasn't too much in depth detail of what occurred that would have involved skirmishes like this.
I looked at what happened in both Halo: Reach, The Fall of Reach, and First Strike, and found some holes to fill in.
Reach High Command is mentioned in passing as being a target of high value, as well as eventually falling by the time Fred and the others fell back to Menachite. Knowing that, I didn't think it was too much of a stretch to imagine the UNSC trying to defend HighCom with such a battle as pictured here, basically just a splinter of the overall battle that was occurring across the planet at the time.