Range-The range given for a ranged weapon is the maximum range to which a typical user can strike with that weapon. The ideal range of usage for a ranged weapon is up to on third (1/3) the range value at which ranges there is no penalty for the typical user. In higher range brackets 1/3-2/3 and 2/3-full range, there are small penalties to accuracy due to the range. More skilled users with Long Shot may use weapons at lesser penalties for longer ranges and can even surpass the listed range of the weapon, some up to 3 times the range of the weapon.
Cover-Whether it is from walls or pillars or trees, anything between a combatant using a ranged weapon and his target contributes cover to the target. This cover is expressed as a percent chance that the ranged attack is blocked by interceding objects. This percentage is based on how much of the target is obscured.
Shields provide cover based on their size. Tiny shields provide 13% cover, small shields 20%, kite shields 30%, large shields 45%, and tower shields 67%.
Ranged attackers can take a penalty to their attacks to reduce the cover provided in what is called a Called Shot.
Called Shot-A called shot can be used made either to reduce the effects of cover or to increase the chance of hitting a particular part of the target’s body. It does this by taking a more risky shot, which is reflected in a To-Hit penalty on the shot. The change to cover or chance of hitting a targeted region is changed by 5% of the current chance per To-Hit point (a -5 provides a 22.62% reduction to cover). The math is demonstrated more succinctly here.