KHPike
I found differences in the losses, when attacking a castle and town. Therefore the calculation cannot be completely ignoring the settlements defences. But you may be right that it does not place sufficient emphasis on the defences.

Given the odds you faced in your Toulouse assault I think you did quite well. I doubt if I could have done any better.

Nebuchadnezzar
I run the original game with patch only on VH/VH. No other mods, fixes or cheats. I am waiting until after the next patch before considering if any fixes are required.

I also have used auto resolve more in this game than all the other games put together. In M2TW you often achieve more favourable results, especially in the early game or when using a larger attacking force of low quality troops against a small garrison. This is partly due to the new calculations used and partly due to the losses from the tower defences when manual fighting the game. In the later games, auto resolving has less an advantage, due to a bigger choice of siege equipment available and therefore greater flexibility to match your tactics to counter the defences.

Foz
Unit Stats.
I have rechecked my original post and you are correct there is an error.
The Town Militia, Hobilars, and Militia Achers are all standard units with no upgrades. The Armoured Swordsmen have weapon and armour upgrades giving them +1 to attack and +1 to armour defence. The Retinue Longbowmen has heavy mail armour and also experience 2 (from the woodmen guild HQ).
All the above details were correctly quoted.

The Feudal Knights also had weapon and armour upgrades, which gave them
Attack 11, armour 8, skill 5, shield 4, Total 17
And not
Attack 11, armour 8, skill 5, shield 5, Total 17 as I quoted. Sorry!

Hobilars vs Town Militia

Unit size
This could be argued both ways.. The town militia has more men per unit (8 x 75) but the Hobilars have more units (15 x 40). Both attacks used 600 men.

Against melee garrison
The Town Militia has a spear bonus + 4 verses cavalry (2/3rds of garrison) making attack 9. This does not apply to infantry (1/3rd garrison), leaving them 5 with these units. This would average out at 7.67 giving them a 0.67 advantage over the Hobilars..
Their total defence is the same as the Hobilars but mainly in shield, which only applies to front/left. If attacked from the other two sides they have almost no protection. Hobilar defence is mainly the more effective armour (applies 360°).

Against missile garrison
The Hobilars hits with 7 giving them a 2 advantage over Town Militia. Since the crossbow missiles are armour piercing, this gives an effective protection of 2 (360°) for the Hobilars verses 3 (front/left) for the Town Militia.

Both have a base moral of 3. Both will rout when they have lost a certain percentage of their numbers. Since the Hobilars are faster, they are less likely to suffer further losses whilst running away. Their speed will also get them past the towers / missile fire into a melee with fewer losses.

There is not a lot of difference between these units. Personally I would have put my money on the speed and flexibility Hobilars for both attacks. Whichever way you calculate it the Town Militia should not be better than Hobilars for both attacks.
The only theory that does fit the order of losses is to assume that the defenders are missile and the losses are ordered according to their missile resistance. This may not be an ideal explanation, but so far it is the only one that fits.

One of the problems with tying to find out what factors CA use in these calculations is the random numbers applied to the results. This suggests that there is not much point in CA spending a lot of time and effort (therefore money) developing complex formulae. Why calculate a units losses to the second decimal place, and then apply a massive random factor that make all the accuracy worthless.
They are much more likely to do a rough defence / attack average for both sides, season it with a few unit size / environment / unit type factors. Stir it all up with a set of random numbers and serve with a fanfare. Whilst the player simmers at the results.
Grouping all defenders (with towers) into one type of attack (missile) would simplify the calculation. Would they really go to the trouble of differentiating and allotting different factors to all the various types of attack.
e.g. Melee, spear bonus 4, spear bonus 8, armour piercing, normal arrows, ballista bolt, exploding shot, phalanx etc. etc. etc.