Leonx, I have heard SACDs where the imaging is bloated and overgrown as you suggest. Other disks where the imaging appears to be right on the button. My experience is that the bloated instrument images is mostly on SACDs that are remasters of old tapes from the 50s, e.g. Dvorak Cello Concerto with Piatigorsky/Munch, or Starker on Bach suites.
This may be just a case of conscious over-engineering of old master tapes by sound engineers that should quite frankly consider visiting a concert hall before indulging in any more fantasy pastiches of unrealistic hyper-realism.