Second that.
Additionally, some form of color-coded indicator (like highlighting the very fine circular border of each unit) of creatures which a particular Sov or Champion summoned (when I select a Sov/Champion) will come in handy which I'll explain in a bit.
a) When I join stacks and split them later according to who belongs to who, it'll be much easier as opposed to taking a look at the levels and trying remember all those details prior to stacking them as they all have the same names/titles (I wish we can change our units'/Champions' names if not at least the ability to put in nicknames beside their names). On top that, if you split stacks and some creatures are greater levels than your Sov or champions, then they lead the stack. Which IMHO, doesn't make sense. I want my Sov who can move 5 tiles to be able to fully utilise his Organized ability with my strongest summoned creature/unit compared to a creature who can only move 2 tiles and leading the stack with my Sov in it.
If you happen to have creatures that belongs to your other Champions and they die from aother battle far away, at least you know it's not their summoned creatures who will disappear in your stack (or will they? haven't tried it yet but the spell description did say only one kind of creature per caster, but if he/she's dead, then the 'enchantment' should go too) suddenly when you are about to storm a settlement. This could quickly become FUBAR if the AI is so inclined to come out and 'play' and you are caught with your pants down without your MVP.
My 2 cents. Oh , I also believe combining individual units into squads, parties and companies should be possible as well instead of disbanding and trying to make those veteran level 8, low level weapons single units prove their worth by going up against level 10 creatures with no chance of surviving at all (even with 45 hitpoints in health) I mean if a big part of the RPG component of this game is levelling-up, I would like to teach my old dogs new tricks (get upgraded weapons and be able to train in a group). Bring them back to settlements, pay bit or a lot more in resources depending on the weapon level disparity and take lesser turns to become a tight company (as opposed to training new units) before coming out bigger and better. Only drawback is: they may groan and moan and bitch about how they 'only work alone'.