2) the ironshields are not the heaviest fighters, that would be the iron guard and the doomchrushers, and they need to wear a full body armour.
if you make the shields bigger, the Dwarfs won't fit into the rank...
Also, in warthrone rules, you distinguish between medium and big shield, and these have only access to medium shields. Iron guard has the option for big shields, so the big shields are kept for them and when looking at the figs it has to be obvious which are big shields and which are not.
Reagrding ranking, we are really making sure that the units which can form from the warthrone rules in closed formations (like a square formation, as opposed to a horde formation) are easily ranked in closed formation, as we have received a lot of feedback of how difficult it is ranking up the Apoc warriors!