ahhhhhh....could it be the reason the car continues to drop is because when you move the jackstands further back...not only does it change the pivot point...but greatly increases the load/weight in front of those jackstands....
think about this...if what you say is true...you would see a GIANT gap forming somewhere....but I bet if you watch or measure your rear bumper height...its coming further off the ground
of course...just my take, I've never had any professional lessons
BTW...stay tuned..I'm about to unveil my new stealth upper shock tower support.....for street application front coilovers