Dont look at the enemy's model look at the symbol beneath it (looks like an almost complete circle sans the back part when you select an enemy). The idea is to stay just at the end of the border (almost on the backside but still count as lateral) for lateral hits then move to the borderless part for backside atack. Unlesss the tank is moving the enemy switching from back to side and viceversa can be done by a single lateral step instead of wasting time moving extra distance.

Also remember that some enemies have a full circle when selected which means that every side counts as optimal position, so feel free to land moves as you want