You should stand where the melee stand...generally you won't get tailswiped (you shouldn't anyway).

Do you know if there are issues with Coil? Kevee said no, and frankly I wouldn't have thought down the melee train except he insisted there was no reason not to.

Thinking about it, it makes sense.

For primals,

Ifrit - melee is a nono, the knockback is stupid.
Garuda - melee is a tossup. I personally like it, because her melee aoe seems to interrupt me less than her ranged aoe (go figure). However, melee during plumes lets you miasma the plumes, so no reason not to.
Titan - same thing, every melee needs to move for plumes regardless, and you move just as much as if you were ranged.

For AK,

Cthulu - No reason not to be. Just don't face the add towards tank or healer
Demonwall - Melee is fine until bees (if you get bees), and then just stay away from the tank.
Gargoyal - You want to be in melee to not have to move when imminent destruction occurs. Make sure to move out for the beam and add. Should be on side and not butt to not get tailswiped.
Adds - No reason not to be, for succubus no reason to be either, for everything else, be on their butts so you dont' get cleaved.

People put up Bio II because it lasts the longest.

For me, I don't care, I usually use miasma cause its the button on my bar first lol. To be fair though, it DOES line up better with BIO II, because if you miasma first, it will have same duration as bio I, and you will have to choose or clip to refresh both.