Yes, your guess is correct. The units "holding the shoulders" were attempting to keep the breach in the lines from opening further. They were trying to pin the Soviet break-in forces for two reasons: one, to keep breakthrough forces from being able to maneuver into their rear areas and potentially encircle them, and two, to limit the size of the hole Soviet exploitation forces would have to move through. Keeping the penetration small, and keeping the break-in forces pinned in place, would also generally make it easier for the German mobile reserve to plug the hole and destroy the break-in units.