[Aerich]

Sneak attack damage is applied any time your rogue makes a first attack from a flank or rear position. Once sneak-attacked, enemies tend to attack the rogue that sneak-attacked them, after which (as makes sense) the rogue cannot sneak attack that enemy any more, unless that enemy switches its attention somewhere else.

To get more out of your sneak attack, you can switch targets often, in theory sneak attacking a different enemy every round. While that may increase the amount of raw damage your rogue inflicts, it may need more micro management (e.g. by setting your autopause feature to pause after the end of every round so that your rogue can switch targets without wasting any time), and may also be less efficient in the sense that it is often better to kill a wounded enemy quick.