Slitherine

In the first photo the Muslim Light Horse (Javelins) unit have lost 10% of its men (114/126) and is disrupted. In the second photo, the same unit have lost over 20% of its men (93/123) and is still steady.

I think, it should be the opposite. The unit with the most casualties must be disrupted etc.

The unit that took more casualties is indeed likelier to fail its cohesion test, but it got lucky. It happens.

It reflects well the fact that IRL the number of casualties is a major factor in the morale of a unit but not the only one.

One possible modification of the Disruption state is to be equal to 1/3 casualties of a unit.
The Muslim Light Horse (Javelins) unit with 126 men strength could be disrupted when loose the first 42 men. And the same for the rest morale states (Fragmented and routed).

No need of any modification.
Morale state is not solely related to fractions of casualties.
There are lots of examples in History when a 'unit' never gave up fighting, despite or... because of their numerous dead and wounded comrades. And the inverse is true too : other units quickly lost heart.

One more thing i have noticed in the game so far is the disruption of a steady unit, when it falls back one hex. Steady unit in full strength away for the battle for many turns.

You mean that your unit was out of charge reach of any non-light enemy unit, whether or not that enemy was actually in a position to charge ?

The unit was one hex away from the enemy unit in open ground. It disrupted and in the next turn, the enemy unit charge and fragment my unit. I was surprised, because i wanted to retreat and avoid a mismatch.

Falling back near enemy is a risky manoeuvre, so the unit always takes a Cohesion Test when within charge reach of a non-light enemy unit (manual, p. 65).

So, a unit must be two or more hexes away to fall back without a Cohesion Test. I was unlucky one more time.

It's actually less precise than that. If you check this post you'll get a better understanding.

viewtopic.php?f=477&t=95234

I thought it was :

1) when enemy face you ready to charge :
≥ 3 squares if enemy = infantry, as they can move 2 squares forward (APs = 10)
≥ 5 squares if enemy = cavalry, as they can move 4 squares forward (APs = 16)

2) + an algo when the enemy "is not actually in a position to charge"

I swear I've been 3 squares away from infantry and taken CT's when falling back.

So, it is unpredictable