It's always going to be somewhat speculative given the lack of detailed information. Snorri Sturluson descibes a shieldwall that is 5 ranks deep, but that's writing centuries after. I assume the formation has to be deep enough that the enemy can't easily punch through it, so I went with five ranks, with the front 3 or 4 actually fighting and those behind throwing rocks and missiles.
I imagine in reality, depth would be variable. You may thin your line when outnumbered to match your opponent's frontage, or have more depth where you expected to breach the opponent's line, the better to exploit it.
I had planned to ultimately add some 'straggler' bases to the rear of the bases to give a more irregular feel, and these could be used to have some kind of game effect depending on rules used. Though, as these would be largely decorative, and the project is pretty ambitious as it is, I don't know when or if I'll get round to them.