again vs on top of that

again

adv
  • Another time; once more. 

  • I ask again, I say again; used in repeating a question or statement. 

  • Over and above a factor of one. 

  • Back (to a former place or state). 

  • Moreover; besides; further. 

  • Here too, here also, in this case as well; used in applying a previously made point to a new instance; sometimes preceded by "here". 

  • Tell me again, say again; used in asking a question to which one may have already received an answer that one cannot remember. 

  • Used metalinguistically, with the repetition being in the discussion, or in the linguistic or pragmatic context of the discussion, rather than in the subject of discussion. 

on top of that

prep
  • Also, additionally, moreover. 

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