Why didn't the Chinese attack Hungnam during the evacuation?

Question

The Hungnam evacuation was a notable event during the early years of the Korean War. Retreating to the port of Hungnam from the recent defeat at Chosin Reservoir, UN forces managed to evacuate about 100,000 troops and about 86,000 refugees to South Korea, in what's also known as the Miracle of Christmas. This was partly due to the lack of any large scale enemy attacks.

Why didn't the PVA or KPA attack during the evacuation? The source that Wikipedia uses, Mossman, Billy (1988). United States Army in the Korean War: Ebb and Flow November 1950-July 1951, offers these explanations:

None of the enemy strikes on the perimeter did more than penetrate some outposts, and counterattacks rapidly eliminated these gains. So far, all action appeared to be only an attempt to reconnoiter the perimeter. Several explanations for the enemy's failure to make a larger effort were plausible. The bulk of the Chinese in the Changjin Reservoir area apparently were taking time-probably forced to take time-to recuperate from losses suffered in the cold weather and recent battles. All enemy forces undoubtedly were aware that the X Corps was evacuating Hungnam and that they would be able to enter the city soon without having to fight their way in. The contraction of the corps perimeter probably forced the enemy to repeat his reconnaissance. Artillery fire, naval gunfire, and ample close air support may well have prevented the enemy from concentrating sufficient strength for strong attacks. Whatever the reasons, enemy forces had not yet launched a large-scale assault.

That is:

• The Chinese were recuperating from losses
• The rapid contraction of the defensive perimeter forced repeated reconnaisance
• Fire support prevented the enemy from gathering forces

These are plausible - particularly since the 9th Army Group was badly mauled during the previous battle - being "put out of action for three months". Nevertheless, these are conjectures, and I was curious if there's more solid evidence for the lack of large scale attack.

Answer 1

The retreat from Hungnam was an aftermath of the Battle of the Chosin Reservoir. In that battle, the Chinese had lost 40%-50% of the 120,000 men they had committed to battle against 30,000 American Marines and infantry. By the time these forces reached Hungnam, they were joined by about 70,000 South Korean troops. So the combined "Allied" forces actually outnumbered the remaining Chinese.

Once the Chinese approached Hungnam, they faced a new problem. Per the wikipedia article:

Against the strong naval gun fire support provided by US Navy Task Force 90, the badly mauled 9th Army was in no shape to approach the Hungnam perimeter."

And American airpower had also been a factor in intensifying the Chinese losses on the move south. The greatest concentration of American planes in North Korea was at Hungnam.

The Chinese had accomplished their main goal of driving the American "spearhead" away from the Chinese border. They had no reason to take on the combination of American soldiers, South Koreans, ship artillery, and air forces available for city fighting where the numerically superior defenders also had the advantage of the protection of buildings.