Although all pairs of stereo speakers have dead spots in certain frequencies and certain locations, pointing your tweeters and woofers (the front channel speakers) inwards like that is likely to lead to a small sweet spot for stereo reproduction.
A subwoofer usually begins to lose its lack of directionality above about 150Hz. By about 300Hz you can generally hear where it is located. The exact frequency where this becomes audible depends on the room dimensions, the subflooring, and the damping material (like carpet, upholstered furniture, curtains, and acoustic panels) distributed around it.