I believe that as you increase the offset between the coils you increase the top and bottom end response (which could also be perceived as midrange reducing), as well as getting more clarity and pick definition. (Essentially it begins to gradually acquire some of the tonal properties of a single coil)
Yes, this does decrease the effectiveness of the hum-cancelling, but there is a practical threshold beyond which it becomes noticeable, and none of the BKPs are anywhere close to approaching that.
By the way, the majority of the range feature offsets of some sort, only very few are totally symmetrical.