on top of

In addition to, following closely on, as in Several other benefits are being offered on top of a better salary , or On top of the flu Jane caught her sister's measles . [c. 1600]

Also, on top of one another . Very close to, crowded, as in I didn't see her until she was right on top of us , or In these condominiums people are living right on top of one another . [Mid-1900s]

In control of, fully informed about, as in The weeds were terrible, but the new gardener was soon on top of them , or Our senator always manages to be on top of the issues .