still at loss in understanding this...

[Pocus]

mmh, and so do you think that its normal that half of the group (the unengaged part) sit iddly in the rear of the formation (with 3 javelins still unused), and watch their comrades die in melee, without using their javelin? We know that its surely not the fear of doing some losses by friendly fire that can motivate them in doing nothing so why are they sitting on the grass?

They are in range yes, they have javelins. They dont use it. They wait, and wait and wait. If the enemy finally rout, the whole formation resume the pursuit, and can fire (somehow). Otherwise they just fill the ranks of the killed. Dont make sense.