As for LE snipers vs Army snipers, Army just wants them dead, LE needs instant paralysis seeing that typically their target would have a direct hostage
Not only that, COM yields a larger target. Current sniper engagements for military snipers are regularly out past 700 yards. A shot to the body is much more likely to hit than a shot aimed at the head.
LE snipers average shot distance is under 50 yards. At that range, most environmental conditions will not effect a POI. If a military sniper has a combatant in his sights inside of 100 yards, he won't hesitate to take a head shot.