Apparently, this isn't a bug, but rather a simple rounding up using the formula [integer part] + 1, without checking if the number is already an integer.
if lurkers attack, increasing the attack of their hero increases the damage.
and there is no damage calculation if they attack in melee.
The damage from a curved arrow/melee/through walls can be calculated, but it results in a lot of calculations. I need to think about how to incorporate this neatly.