on top of that vs over and above

on top of that

prep

  • Also, additionally, moreover. 

over and above

prep

  • in addition to, supplementary to 

adv

  • More than is necessary or than expected. 

  • more than is required e.g. by a contract. 

  • Supplementarily. 

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