Ideas!
There is a game, Age of wonders II, that allready has nice tactical combat with things mentioned above! Actually, Age of wonders has ALL the features mentioned above! I wonder if you28 actually had that game in mind!
As I recall, AOW tactical combat also had (with all the previous points):
1) sieges - with walls and various magic protection, also more siege weapons
2) strength of long range weapons diminishes with distance, also it had different ranges with different weapons. Actually, it was long time ago, so I don't remember if it was strength that is reduced or the probability of hit, probably later, but nevertheless...
3) Flying units (and different type, floating units, but that is similar to ground units)
4) Units were using theirs future move (action) points for counterattacking. In Elemental, unit can actually double their attacks per turn (attack and counterattack)
So, the tactical combat in AOW was great, only thing lacking was the AI, which was rudimentary, it could have been exploited easily (But, than again, so can it be in Elemental).
The thing I like in Elemental tactical combat are squads, they add something new, just that! One thing I would add is that the damage done with the attack and counterattack is simultaneous, for a start, so that I can't kill 3 units in a turn without they even had a chance to land a blow!