1. exchange the subwoofer and left front speaker.
2. make the distance (from back wall) between right and left speakers are even.
3. do not toe in first
4. test any improvement.
5. if not, move 1 cm forward of your right speakers. Or toe in a bit of your left speaker to make it balance.
6. then adjust both speakers to make the vocal sound in the center.
just my 2cents. dont hit me if i am wrong!
hope it will help.