So if a person is using investiture without the aid of an external tool, it's physical? Which would mean the vast majority of investiture use we've seen so far has been physical: Allomancy, Feruchemy, Awakening, AonDor, ChayShan, Dakhor, Surgebinding, and Sand Mastery.
Mechanical investiture use is channeled through something else, not through the actual user. Would that include Hemalurgy and Soulforging?