The sovereign aparently provides at least a morale boost to troops, which is affected by the choices made when you create the sovereign.  Is this morale boost for all troops, or only for troops in the stack with the sovereign?

i would suggest having the morale boost, and any other modifiers the sovereign (and/or any "heroes/champions") provides to troops, be distance-based - e.g. troops in the same stack with the sovereign get 100% benefit, then as troops are further away from sovereign the benefit declines in some sort of geometric progression.

This will add to the strategic decision implications of where to position your sovereign.