thanks for the knowledge sharing...He paid an extra 486.3. He will get back 1.00% or 300 on 1 Sept. So net he paid extra 186.30. This to use your words “eats into” his 3.0% coupon over 26 months for a clean cut off yield of 2.70% pa.
actually I think at the end of the day, all it matters is the 2.7% effective yield bah. MAS won't be making mistakes in their calculations so just trust they will do the necessary (deductions, refunds, coupons, etc.) and just sleep easy
but good to learn!