Good question but I think you can find all these answers by playing alone.
Surprisingly if you want i can share some info on damage reflection too.I have experimenting with it along with potency ,frostbite ,stun,petrify and demolition.All these perks are good if you on some specific heroes.Right now I have three heroes(Cadmus,Perseus and Artemis) that have above 50% damage reflection(it is a very good perk for a defender but not for attacking heroes)
Don’t know about it but I am sure it means 20 % DR will reflect 20% of the damage done to hero.
it is a AOE cone but its arc is small that it only hit two three archer or similar small units.For structures it hits only a single structure(my guess they are big and takes more space than spear man,sirens ,archers like small units) that is in front of hero like barricade takes damage whenever Apollo tower hits my hero DR reflects some portion of that damage back to barricade as it is right in front of hero.
Damage from DR can be avoided but there is only one scenario where I have seen it gets reflected .
A Hero can reflect damage from an Ancient defender equipped with DR items.
But don’t whether its reflects elemental damage or physical damage( @CaptainMorgan can you confirm this?I have no idea about it but you are the only one who can answer this question.)?
Actually it does both. Reflector also takes some portion of damage while reflecting the damage and that is because game does not have 100% DR bonus as a perk.