This significantly affects the levy size, e.g., -50% at 0 skill and +50% at 20 skill.
Martial skill: 5% * (martial skill - 10).
Levy size modifiers is the sum of modifiers from:.
Additional buildings levy brought by buildings.
Holding base levy depending on the holding type: tribe, castle, temple or city.
Holding Levy = (Building levy) x (1 + Levy size modifiers) x (1 + Tribal land bonus) Their size depends mostly on the holding type, buildings, and the direct owner's martial skill. The holding levy is the levy of a particular holding, and it determines demesne and liege levies.
5.3 Setting Ideal Levy Laws (Without Conclave active).