OK... I come help u...
First of all, big screen doesn't mean good. Make sure it is the right size or else, you will feel dizzy...

Your room size is only 12ft. minus your sofa and minus your sitting position, you probably ended up around 10ft.
So, go figures your screen size.

Regarding your arrangement

C - You will have better lighting control since your screen is tucked inside a corner. The problem you might face is the speakers. It might bounce here and there...

D - You have a cozy corner... and this time, your surround will be better, front speakers will be more controlled.