[Hectic]

over 2 or 3x it becomes more dificult to aim with both eyes open.
also depending on yer dominant eye can make it more dificult.
i aim with both eyes open on 3x and iron sites all the time but it took alot of practice, i am a right handed shooter but i am left eye dominant at first when i tryed to do it the scope would become blury and distorted and i couldnt hit what i was aimin at if you payed me.
so i found out that i was left eye dominant thats why i could see everything well on the left eye but the scope would be all messed up.
if find that if i squint the left eye a lil bit it makes the right eye take over and the scope picture becomes clear and i can still see everything else outside the fov of the scope. After a while of doing this i have to squint less and it becomes easyer over time.

to test yer eye dominance you can either point at an object baisicly use your finger as a front sight post or you can put you hands together crossing the two thumbs and two pointer fingers to create a hole to look through.
the point or line up the hole infront of an object across the room with both eyes open, then close one eye and the the other. when you close your right eye if the object seems to move out of the circle or to the side of your finger then you are right eye dominant and vise versa.
as blackthorn said try to focus on the target and then bring tue sight up in front of your eyes to aim at the target rather then lookin through the site to aquire thebtarget so aquire target then aim