Extraterritorial costs and foreign income

Hello, I wonder if you can help. I live and work abroad but am a UK resident for this tax year based on the SRT. My foreign employer has agreed to pay a % of my salary to cover my extraterritorial costs. I see that there are special rules for this situation (e.g., https://www.gov.uk/guidance/special-tax-rules-on-foreign-travel-490-chapter-7) but as I receive a % of salary rather than reimbursement for each individual expense, I wondered how this would be dealt with by HMRC within my self assessment return? Many thanks in advance.

Hi JohnnieHuman,
This is a round sum expense allowance EIM05100 - Employment income: round sum expense allowances and would be assess/allow with
actual allowable expenses being claimed on SA return.
Thank you.