Current touch attack AB implementation on Arkhalia:

BAB + size modifier + ability modifier if higher than 0 + nature sense (in nature areas only) + bane of enemies (against favored enemies only) + epic prowess feats + normal/greater/epic weapon focus (spells) + point blank shot (ranged only and within 5meters) + “effects”

ability modifier is strength for melee or dexterity with weapon finesse if higher or wisdom with intuitive attack of higher
and dexterity for ranged or wisdom with zen archery if higher
and charisma for both with sanctified or vile strike against creature of correct alignment

effects are “capped” bonuses to attack bonus from spells like bless and activable feats like bard song