Move your sub

It would seem that with the subs further out in the room they would need  to be played louder. 

ozzy

Your optimizing the bass time arrival if subs near plane loudspeakers occupy you could also place behind listener or on sides if physical distance is near same as seated listener is from both speakers and sub. You could keep subs physical distance correct for time integration and pursue boundary re-enforcement that most subs require. Or use multiple sub systems this gives better measured response in most rooms lower distortion increases system output.

Placement depends to some extent on what subs you are using.  With the Vandersteen 2wq subs that I use, I need to keep them near each speaker as the subs reproduce frequencies high enough to affect imaging.

Proper sub integration starts with the room position that gives the smoothest response as measured at the listening position.  For my sub it happened to be just outside one of room corners in front of me.  
From there you can adjust continuous phase (a required feature), polarity (a required feature), crossover and level to phase and time align with your main speakers.  The result is seamless, non-directional perfect subwoofer integration and optimized power response.  

@miner42 

https://www.youtube.com/watch?v=k3hRbm7KU1U