Yes, describe the actual proposed assignment, including any continuing responsibilities already contemplated. Keep unresolved plans clearly identified. Two record-keepers hold the answer between them. The company's own files establish the corporate relationship and the employment abroad; the operation's business plan and staffing schedule establish what the later role would govern. Work out which side is missing a document before drafting a letter that describes both. A description spanning periods nobody has committed to invites a reviewer to test the weakest part.
Avoid an incomplete time horizon
Show when duties and support would change and which records establish the plan. Do not present only the opening phase if materially different work is expected afterward. The reviewer needs the proposal as it actually stands.
Records settle what narrative cannot. An organizational chart dated to the proposed start, a staffing plan with headcount and hire dates, a lease or service agreement showing the operation exists as described, and the foreign payroll register covering the qualifying year each answer a distinct question. New-office petitions receive a limited initial period and are afterwards reviewed against what the office actually did, so a document promising a structure creates an expectation somebody will have to meet.
Keep the commitments modest enough that the company's own officer would defend them a year later, and mark clearly which items remain proposals.