Yes, the documentation is not clear about this. We've had to work closely with LB for quite some time to solve this conundrum. Here's the key:
The Registrant Contact of a .ES domain name may either be a natural person/individual or a company. However, the Admin, Technical and Billing Contacts must be natural persons/individuals only.
-If the Registrant is a person, then the Registrant and the Contact are the same and they have the same es_form_juridica, es_tipo_identificacion and es_identificacion
-If the Registrant is a Company, then it gets more complicated, because the Company can't be a contact, the contact needs to be a person. So you have to supply two sets of fields, one for the Registrant (Company) and one for the domain Contact (person).
Am I making sense?