Plate Manica

[Tarbicus]

Wasnt the legionary plate manica introduced during the dacian wars to stop the significant injuries recieved from the dacian falx?
And wasnt the leginary helmet reinforced on its top during the same period?
I think therefore the leginary fighting outside forces had to defend mostly against downward cuts and chops and might have therefore favoured the downward overlap.

Manica have been found outside Dacia, in Britain. A well made falx would at least cause serious trauma beneath the armour, especially compression damage to the neck from a severe head blow (can't remember my source - it's based on tests done). Would a falx's downward stroke be more inclined to return back, or would it still be going forwards on contact? If it's purely down I don't see how upwards or downwards overlap would particularly make much difference, but the manica would be still be good for other weapons. At least an upward overlap would take a weapon more towards armour and not the more vulnerable sword hand.

Dacia aside, one of the greatest threats to a legionary's arm would be from a spear, in which case the blow would surely be coming in from the front anyway. In fact, I'm sure you could probably still include Dacia in that.