On Top Of Meaning

(idiomatic) Fully informed about, and in control of something; up to speed with.

Example: Atop
Very close to, in any orientation or in time.
  Living on top of one another in a refugee camp is stressful.
  At peak times, a telephone operator must handle a number of calls, one on top of the next.
  . . . and on top of all that, I got a puncture!
  I have sorted out the problems and am now on top of the situation.