The below quote is from an installer from the Chicago Area IIRC. He is a dealer for HAT's and has just recently finished an awesome installation for paste36prsnte46 that you can see over at DIYMA. It relates to our conversation about overlapping the sub and midbass.
One thing I have found that a bit of overlapping on the front midbass/subass will help bring the image forward and help sub localization problems.
*Note: Only if the front speakers are capable and the sub is not too far out of alignment & phase.
It is not the same for every car, but something to try."