I want to give you another option: Rather than just the typical speaker repositioning or adding absorption center image between your speakers, you can try an electronic solution...
What I enjoy is connecting the left and right channel cathodes of a gain stage together with a capacitor. This has the effect of canceling the mono image, and expanding the stereo image. Attention to the capacitor value will allow choice of the cancellation corner frequency. Typically only a small value capacitor is needed. This may even give the perception of 'tightening-up' bass response.
What I enjoy is connecting the left and right channel cathodes of a gain stage together with a capacitor. This has the effect of canceling the mono image, and expanding the stereo image. Attention to the capacitor value will allow choice of the cancellation corner frequency. Typically only a small value capacitor is needed. This may even give the perception of 'tightening-up' bass response.