Is it okay sitting exactly at the rear wall ?

[dazkyl]

I can easily move my sofa forward for watching movies. My sub is the at left front corner near my left front speaker , and i noticed some rumbling coming out of the sub when i sit exactly at the rear wall. When i moved it a little bit forward,the bass was smooth and punchy. Can i stay at the rear wall and turn down the volume of the sub a little bit ?

Thanks. (Current sub gain knob volume is set at about 9'clock)