When you look at brace positioning the first consideration MUST be structural integrity.
For example when moving the "X" you need to be sure to keep 'at least' the front ends of the bridge wings supported by the rear legs of "X" or the bridge WILL roll. So tonal pursuits must be within the constrains of function. Moving the "X" forward takes the soundhole with it, so yes this effectively increases that area of the soundboard which I feel is the most important in relation to sound generation. But the trade off with anything more than just a small shift is that the spread of the "X" will need to be altered to capture the bridge ends unless the scale length is altered, or the bridge wings are extended, all of which will have an impact upon integrity and tone.
I won't go with the "More Bass" theory simply because I do not see how the action of moving the "X" forward would do that of itself. To my mind the best way to think of all this tonal stuff so you have a starting point in understanding what is happening with bass and treble response, is to think of the waves of an oscilloscope. With higher frequencies the oscillations are short, sharp, and obviously more frequent. Leave a top thick, over braced, and stiff and chances are that when it is excited by string energy, kinetics will release in short, sharp and frequent oscillations of that top...it will be OK at highs but little else.
Take the same top and thin it down to frailty carving away the bracing until it becomes loose and flexible. Such a top will now move in much large oscillation when exited, the energy would be expelled in long, blunt and less frequent oscillation making it better equipped for bass frequencies or low Hz.
What our challenge is as builders, regardless of the bracing pattern or positioning employed, is to find the middle road between those extremes that will produce the most efficient use of available kinetics, and then to apply skills and understanding in the assessment and bracing of each top to produce a bias toward the 'tonal' out put we desire for an acceptable investment of that efficiency....nothing more to it really.
Cheers
Kim
