I'm going to add my 5c here. I spent last summer as a part of the British Guard at Fort York in Toronto. For demonstrations we did skirmishing tactics for the audience, so we trained as stated in the period manual for the British. Skirmishing according to the manual is not using cover. It is open order combat, 3 paces between men, two ranks five paces apart, both kneeling. One rank fires, the second leapfrogs ten paces forward (since they are 5 behind the front, they will end up five in front) and then kneels. The new front rank waits the rear rank to reload before letting off shots, and begins to reload while the rear rank leapfrogs and so on. You are allowed to individually aim and fire on your own time, but the entire practice is still quire rigid, you fight in a spread out line (hence skirmish line), but you still are largely in the open and you maintain a 3 pace spread between men, you don't go running for cover. Think of Napoleon Total wars fire and advance option, that is essentially how skirmishing was suppose to be done, going forward or backwards.
The units that tended to be more skirmishy like many people complain about in game were usually irregular forces, and possibly elite rifle units. For example the Quebecois during the seven years war in North America fought in this "indian" manner, the british grudgingly giving credit for their effective use of trees and rocks in covered ground but making a point to criticize their poor line fighting ability if cover was absent. However European skirmisher were much more controlled than the irregulars, at this point as the art of official skirmishing was still quite young (first appeared in euro armies in the 7 years war with Austrians I think), and the highly ordered method of battle that was common was hard to give up.
If you want realistic skirmishing, there needs to be more order in it. European skirmishing is much more rigid than many would believe, the commander is still in charge and the formation had to be relatively close together in order to hear his commands over the noise of the battlefield. They had to be close enough to form up into ranks and form a square if Calvary was bearing down on them.