The B-1A was optimized for low level penetration from the start and not for high altitude as the article states. I worked for Boeing at Palmdale Plant 42 and then later at Edwards when the first prototype was flown there. Boeing was responsible for the weapons and navigation computers on board the B-1A. The B-1A had terrain following radar that was set for 200 ft. The B-1B had more electronics and the CG was shifted aft so that terrain following had to be raised to 400 ft. because the tail-heavy B model couldn’t execute abrupt pitch changes, necessitating the higher altitude terrain following.