on top of
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.
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]