I too have experienced the bass tightening qualities of WM's cables - so I'm not saying they don't do it- just that the explanation lies elsewhere. Is it possible that they are reducing the group delay aparently inherent in analogue electronics ?
If that were the case, then it would have nothing to do with room modes. Another explanation would be a reduction in bass output, or a cleaner more extended treble (think of the effects of supertweeters).
For me anyway, i don't do this "tight bass" thing too much. Bass should breathe. Big bass, big warmth and solidity. Low bass will never sound tight - it should not anyway due to the size of the wavelength. Mid bass (80hz-160hz) is where this tightness comes from. Could it be that WM's cables are acting as a high pass and filtering out the low bass, giving the impression of greater speed and less overhang?