- A reference guide and manual in Russian for Heroes 3.

Not quite! The castle wall creates its own penalty! Even if the distance is 5 hexes, but there is a wall, the arrow will be weakened...

Don't mislead people. The castle wall halves the damage in addition to the distance.
Because these are not the same thing.

There are two mechanisms for calculating ranged damage - one depends on the distance (10 hexes), the second - on the presence or absence of a castle wall. During a siege, most ranged units initially shoot at a quarter of their strength. And these mechanisms work independently for each unit, and do not apply to all units. For example, Mages/Archmages do not have a penalty when shooting through castle walls, but they do have a distance penalty. Snipers, for example, do not have a distance penalty, but they still shoot at half strength through a castle wall...

So, all ranged units do not have a penalty when shooting at a distance of 10 hexes or less.
Obstacles on the battlefield do not interfere. But the wall is a different matter. ;)

But if a catapult destroys the wall, the arrow will become direct;)

If the distance is more than 10 hexes, the arrow will still be weakened.