On numerous occasions, I've needed to run away from enemies and retreat to safety by dropping aggro so that the enemy will give up their pursuit. Sometimes, it seems quite easy. Other times, however, the monster seems content to chase me for quite a while before ultimately giving up. I'm curious if there are any general-purpose rules of thumb out there regarding how and when aggro can be dropped in a single-player game (with or without a Follower).
Is it merely based on distance between you and the enemy, line-of-sight, pursuit time, or something else? Does it vary between normal and Champion/Rare/Unique monsters? Are there any other factors that go into it?
While I'm aware that certain class-specific abilities exist for doing this (Smoke Screen, etc.), I'm specifically interested in the general mechanics of how to drop aggro when attempting to run away, regardless of class.