Thank you everyone for the warm welcome and the nice comments! it's an honor to read your opinions!
Acassani, thank you for the observation, I actually looked into the matter before posing my character.
You see the E-11 is based upon the not so ergonomic WW2 british Sten submachine gun. It is supossed to have a retractible buttstock, but most of the time, if not all of it, you'll see stormtroopers shooting from the hip and without the stock. Actually, this is a design flaw from the armor itself, because the helmet is so big on the bottom it would get in the way if you were to lean your head into the stock for aligning sights.
So in order for him to aim properly I had to extend his arm a little bit more, considering his stock is folded into the front of the rifle because of this flaw .
As for the rifle being held with his left hand, I have been playing paintball and shooting guns while running for over 12 years, and whenever we run to the left, for better hip aiming we hold the gun with the left hand, and viceversa when we go to the right
Here is a pic of me while doing so
So I didn't think him holding the gun with the left hand would be a problem, actually I thought it was more realistic because of the way he was running, but I will look further into the posing again to see if I can make it look more fit.