Attack/Defense bonus for units based on the hero's specialization.

I've been wondering for a long time how the attack/defense bonus is actually determined for units that are a hero's specialty. For example: Galtran (skeletons) or Shakti (troll guards). I saw a formula in the physics engine that calculates the attack and defense bonus for each level, and then there's another formula that, according to my calculations, contradicts the first one. I calculated the bonuses for Galtran and found that for every 4 levels, 1 attack point is added, and for every 5 levels, 1 defense point is added. So, at level 30, skeletons will receive an additional 6 attack points and 5 defense points. Is this really how it works? Please explain the principle behind calculating the bonus for units. P.S. I'm also curious about the Logistics and Necromancy skills - the description says that each level adds 5% to the skill. So, if a hero has Necromancy maxed out, they get 30%, and since the maximum value cannot exceed 100%, does the hero only need to level up to 14 to reach the maximum value?