I have never learned to back kick and it is not necessary in currents. As others have mentioned, if you are drifting passively with the current, you body position is irrelevant to your velocity. However, if you want to slow down or move against the current, you need to always remember to have your nose straight into the current. So in one situation, body position doesn't matter at all, and in the other situation, it is critical.
You need to look ahead and "see" large formations you can duck behind, and look for a dead portion of reef that you can hold onto. It takes some skill and forethought to do this effectively.
Generally, you will be drifting passively, with your body positioned with you feet up current and your head down current ( in other words, you are going with the current). But when you want to slow down, or duck behind something or grab onto structure, you MUST be turned to face directly into the current. This is one time when you need to be able to spin around and move FAST.
You want to go from a head down-current position to a head into-the-current position very quickly and smoothly. The sooner you can figure this out, the better you will be at diving in a current.
If you do otherwise and you are drifting head first and you grab onto the bottom, the current has a tendency to flip you over vertically and make things very difficult for you. An experienced drift diver knows that the last thing they want is to be holding onto the bottom with their fins pointing into the current. Birds always keep their face into the wind and fish that are resting also always keep their nose to "the wind".
Knowing exactly what direction the swirling currents are moving and positioning your nose directly into it (when you want to stop) is the critical skill. Environmental clues like bending soft coral and the orientation of passive fish in the immediate area are often very useful.