Do you understand what position this head is very important underdog140! I did fight at one time and if the receiver's head is at the end of it's recoil, there is no shock absorption of blow.
You can move your head by moving it side to side etc. with out moving your shoulders and reduce the impact. If you are at the end of movement and get hit it does not have to be strong hit since impact is 100%, plus how much punishment taken before does add up. That is why it may take months to a year before they can fight again!
They fight minutes but take months to recuperate, what does that tell you!
A hit 4 rounds ago does not go away the announcers say that to get you hyped. It is part of their job.