leg up vs on top

leg up

noun
  • A boost, a sudden improvement; an advantage, an edge. 

  • Assistance, help given to get started or overcome a problem or obstacle. 

  • The act of assisting another's progress over a wall or other obstacle by forming a step for one of their feet with one's hands. 

on top

adv
  • In a dominant position. 

  • On the highest point or surface. 

How often have the words leg up and on top occurred in a corpus of books? (source: Google Ngram Viewer )