I "borrowed" my concept of morale from Heroes of Might and Magic. Basically how it works is for every sphere of creature currently in battle there is a 5% greater chance that each creature may miss a turn because of low morale. There is also a chance to gain an extra turn because of high morale.
When you first summon a creature there is a 5% chance to gain an extra turn because of high morale (105 morale score). Now if you summon any other creatures from the same sphere they will also have a 5% chance each turn to gain another turn. It doesn't matter how many creatures of the same sphere are on the field...just how many spheres are in play.
Now, if you have two spheres on the battlefield (like Fire and Life) then your morale score goes down to 100 (there is only 1 morale score for the entire army). At 100 your there is no chance for good or bad morale.
If you summon a third sphere it will go down to 95 and now there will be a 5% chance to lose a turn because of poor morale. And it continues to go up or down by 5 depending on how many spheres of creatures you have in play.
One other factor in this is characters summoning creatures. Remember, characters can summon creatures and rune summon creatures. Creatures summoned by other creatures or immortals also play into morale. This means a wizard summoning a Wall of Stone would be brining in an earth creature that may add to the # of spheres in play.
And one final note. Immortals do not have spell spheres. They, unlike creatures are unaffected by sphere affinity and they do not lower morale when summoned. This is important when taking into account the overall concept/integration of morale and sphere affinity and its positive/negative affects of using various rune spheres.