The prevailing strategy for the Khe Sahn area was to take and hold the high ground - which has been the Marine Corps strategy since WW I.  There were assaults up 881 North and South in the past with significant casualties (1966 and 1967) by different USMC battalions.  

Because 881 South had a saddle back type summit, it was the home of 2 companies, Charlie and Delta. 

881 North was not populated, as 881 South had excellent fire coverage of the hill.  The overall surrounding terrain was hilly and convoluted - and offered good cover, even though there was considerable de-foliation. 

At any rate, taking and holding the high ground works in conventional warfare, but in Vietnam, where the U.S. enjoyed air and supporting arms superiority, the NVA used unconventional tactics.

The terrain allowed the NVA to move small units fairly undetected, and to harass our emplaced companies with sporadic mortar and rocket fire - usually 2 to 5 rockets or mortar shells at one firing.  

My conclusion was that the NVA had multiple emplaced mortar base plates (82 mm and 160 mm) and could move to one, set up a tube, use  pre-determined aiming, and drop a few rounds on us.  Similar tactics were used for the rocket attacks (mostly 122mm), although because they were not that precise, and not high-angle of fire, they did little damage.

The fact, however, that the NVA had our routes of egress and ingress off the hills registered - i.e., targeted.  This was very evident whenever we did day-work (patrolling during the day) - particularly on 881 South, where there were limited egress and ingress routes.  Whenever one of our patrols left the area, the NVA would drop a few mortars on the egress route - we almost always took casualties..

What did Sun Tzu (or was it Terry Pratchett) say?  "If any enemy has an impenetrable fortress - see that he stays there.."  These were the NVA tactics during our battalion's "tour" of the Khe Sahn hills.