some questions about xp gain

[Forgpelsznart]

1. In the game it says that enemies have to be around my level for optimal xp gain. I found info that it means that low lvl enemies don't get you much xp. What about high level ones, is there penalty for fighting enemies much higher lvl than yours?

2. Enemies killed by your DoTs do they give you any experience? As a lvl 16 I just killed a lvl 25 unique giant chieftain by burn (I got blinded and moved away, when my sight returned he was dead, maybe I have to see them to gain experience?) and my xp bar didn't seem to move.

as a comparison I killed another unique giant lvl25 just before that and my XP bar jumped significantly granting me a levelup.

[ZyZ]

1. In the game it says that enemies have to be around my level for optimal xp gain. I found info that it means that low lvl enemies don't get you much xp. What about high level ones, is there penalty for fighting enemies much higher lvl than yours?

2. Enemies killed by your DoTs do they give you any experience? As a lvl 16 I just killed a lvl 25 unique giant chieftain by burn (I got blinded and moved away, when my sight returned he was dead, maybe I have to see them to gain experience?) and my xp bar didn't seem to move.

as a comparison I killed another unique giant lvl25 just before that and my XP bar jumped significantly granting me a levelup.

AD 1
You won't gain exp from enemies way below your level (like 3+ levels) and there is no penalty for killing high level mobs.

AD 2
There is no penalty for using dots. As to your example, some mobs inherently have higher exp multipliers and not all unique mobs are equal.
Basically all mobs below rare rank have to be killed by you or your summons (doesn't matter how) to get some exp. Rare, unique, boss mobs gives you exp no matter how they die (friendly fire, different AI factions fighting each other). Game simply assume that you had something to do with mob death even if it dies offscreen.

[Forgpelsznart]

Hm, maybe I just read the xp bar wrong, like, really, I thought it was in the same place as before I killed the mob... or maybe it's the fact that the log doesn't say anything when I'm blind that's confusing, i don't know - is there a way to display actual xp points instead of %? can't see anything, even on inspect character there's %

[HousePet]

Killing higher level enemies doesn't really give you a noticeable amount more XP either, unless they have a boss multiplier.