An aimed musket firing a ball between .6 and .8 inches in diameter can be effective (causing a casualty at least once every 100 shots) and lethal against a mass formation at well over 100 yards (although more like 50 - 70 yards if firing at a single man). In the 18th century, however, very few soldiers were taught the fundamentals of aimed fire -- in fact, due to the unreliability of their weapons, they often closed their eyes and turned their faces away before firing (Chandler notes that most soldiers might fire as few as 2 rounds a year in practice). Line infantry was instead taught to reload quickly, mechanically repeating their tasks even when deafened by the crash of musketry, boom of artillery, and exposed to a hail of lethal lead and iron. In these terrifying conditions, 4 un-aimed shots a minute was considered a very good rate of fire.
In fact, while doctrine might call for an initial volley at under 100 yards, it was not unusual even for well disciplined troops to fire much earlier than that -- sometimes beyond 200 yards. At this range, the fire was ineffective.
What about the "company sized target" studies? You may have read one of the "fire a volley and count the holes" studies. They have several inherent problems: first, they were not conducted in battle conditions where an actual target was likely obscured by thick, drifting smoke and where the howl of cannon balls and the crushing sense of ones own mortality were likely to significantly reduce hits -- and the combat stress would only increase as a battle continued. While well-trained veterans would be more resistant, their efficiency would ultimately be severely impacted as well. Second, when under persistent and deadly fire, the men in the following ranks will make themselves as small as possible behind the men in the front rank -- this will leave a surprising amount of 'white space' in a formation where a ball could travel without contact. Third, anywhere from 10 to 15% of hits would be grazing or flesh wound hits that would not incapacitate a soldier, and might not even be noticed in the heat of battle (This, by the way is modeled in the this mod: 83% of musket and cannister hits and 70% of carbine and pistol hits will incapacitate). Fourth, some of the targets used in studies were too large -- as large as 3 yards high. These "studies" simply do not provide an accurate measure of musket lethality in battle conditions. So what would be a more appropriate hit ratio? One figure from the battle of Vitoria is that the British, who had notoriously good fire discipline, fired almost 500 rounds of musketry for each French casualty (note that the term 'casualty' generally refers to any soldier killed or requiring any medical aid, including a band-aid on his booboo).
You will see these considerations reflected in the following ways:
Line Infantry will fire at 90 yards, their approximate effective range against a mass target. At this range, each volley will cause a few casualties. At maximum range, line infantry may engage for some minutes before causing significant attrition. At shorter ranges, however, a volley may be very lethal, and several effective volley is likely to rout poor quality troops, or weaken better trained troops sufficiently for a double-quick bayonet charge to finish the job.
Lesser-disciplined troops, such as Urban Militia and Substandard Line troops, will open fire at 105 yards. At this range, however, they will do very few casualties. At closer ranges, they will shot-for-shot cause about as many casualties as line infantry, however the better training of line infantry, especially line infantry with advanced firing evolutions, will quickly overwhelm in sheer volume of musketry.
Well trained troops, such as light infantry and other musket-armed skirmishers, will open fire at about 130 yards. At this range, they can still cause significant casualties, and this will increase quickly as the soldiers close. They are most effective when kept at range, and engage line infantry from the flanks. They do not have access to 'rank fire', which means that, at shorter ranges, the volume of fire of line infantry will overwhelm them. If I had my druthers, it would be possible to switch light infantry regiments from a true 'skirmishing' doctrine (which is not represented in game) to 'line' doctrine, while on the field of battle. One would allow them to skirmish effectively, while the other would allow them to 'hold the line' and make use of evolutions such as rank fire. This would be a more accurate representation of their actual usage on the field of battle, but does not appear to be possible (at least to my standard) within this engine.