Why is beryllium to boron an exception to ionisation energy?

Beryllium to Boron = decreases instead of increasing (across period) Be: 1s2 2s2 B: 1s2 2s2 2p1 electron lost in boron is in the p orbital which is slightly higher in energy = further from the nucleus than the s orbital = lower energy to remove Same for Magnesium to Aluminium