the front armor is important and there is no doubt for it that must be strongest after that turret and lateral armor , its true that back armor have least of important but having no armor at all is too much trade of. by the way arn't the ammo in tanks based on t-72 stored around turret, won't it make a weak point if they build part of the turret weaker
merkava turret have nothing much . no flammable hydraulic system no stored ammo , its hard to explode it . and the body at the back is thicker than you think and have composite armor , yes not as thick as front a underside but have some protection
about firing from the back , in desert yes you are right but in urban area . many situation happen that they come from fire from all area.
inside Abram
the engine protect the crew from back , if i'm not wrong Russian tanks the crew are higher so the engine won't provide that protection.
wonder how much heavier the tank would have become if they added a layer of composite armor to the back of tank also you must not forget the flaw in the turret of t-72 that make it prone to explosion