Why does slight decrease in IE1 between beryllium and boron influence ionisation energies?

- Boron has 1 more proton than beryllium, there is slight decrease in IE1 on removal of outer electrons - beryllium has electron structure 1s^2 2s^2 and boron has electron structure 1s^2 2s^2 2p^1 - Less attractive between 5th electron in boron and nucleus because, distance between nucleus and outer electron increases slightly, shielding by inner shells increases slightly