The IBB "program" was more a teaching tool to learn how to lift explosively, autoregulate and ramp properly. I said that several times.
There is also the fact that I recently came to the conclusion that different muscle groups respond to different rep ranges and rep style.
Upper body pushing muscles respond best to performance training (low reps, higher frequency, heavy or explosive movements, more sets of fewer exercises, etc)
Lats and biceps respond best to more volume (higher reps), high density techniques (supersets, rest-pause, isometric holds, etc.). They do not require the eccentric portion of a lift as much as pressing muscles to grow and respond very well to eccentric-less training. Basically these muscles respond well to fatigue training while pushing muscles respond to performance training.
The lower body responds to a wide range of reps; from low to high, everything works but you need some variation. The lower body also requires a lot of volume to grow, but a lot of lifting volume for the lower body (if using big compound movements) can drain the nervous system and hurt your gains. So adding volume in the form of a lot of sled work is your best option.
Rear delts, traps, rhomboids respond to moderate reps (6-8)... they are basically at the middle ground of the pressing muscles and the lats.