Not quite. The battlefield zero on a sight is not set for maximum engagement, but for slightly past mid-line.
An additional part of those studies is where they pulled the concept of 'maximum effective range' for various weapons.
Maximum effective range is defined as the range at which the average soldier has a 50% chance to hit a man sized target.
Zeroing a weapon for 250 meters on a weapon assumed to be effective out to 360 meters (Army) or 500 meters (Marines) gives a fairly flat trajectory that should be functional in combat. If you aim for the center of mass, the minor variation in round flight gives a solid chance of an effective hit.
For tripod mounted machine guns, they were frequently set to fire aimed to 'grazing range'. which is defined as the range the weapon's round stays within 1 meter of the ground. Anyone moving at other then a low crawl through that area is in significant danger.
Any soldier is trained to know where their weapon is zeroed, and to be able to adjust their aim based on actual percieved range.
Engagment ranges are also in a flux based on environment, as they are finding the battles in Iraq tened to start at longer ranges in the open areas, and at much shorter in urban areas.
Snipers also have to worry about engagement ranges, because the engagement range is based on how far away you can see and engage the enemy. Snipers are trained to be able to spot things quickly, so they are more likely to be able to engage a target at a greater range, but you can never fight effectively beyond the range where you identify your target.
In WW2, they were still working with training soldiers to adjust sights for various ranges, as opposed to simply setting a battlefield zero. Many soldiers did simply work with a battlefield zero, but they all new how to adjust.
Marines got the nickname of Devil Dogs because the normal Marines were shooting German soldiers in trenches 5-700 meters away when they first got to the battlefields of WW1. They had the lines of sight to engage, and the training to be comfortable engaging at those ranges.
When I was serving in Eurpoe, we trained with the expectation of 3-400 meter engagement ranges because of the terrain. Most of the suggested battlefields in DUST would match or exceed that.