Luploid ACCA SBR 2019

Hello, thanks for your videos and explanation.
I came across this question and I’m not sure about the answer.

Luploid Co issued 100 options to each of Hammond Co’s 10,000 employees on 1 July 20X7. The shares are
conditional on the employees completing a further two years of service. Additionally, the scheme required that the
market price of Luploid Co’s shares had to increase by 10% from its value of $30 per share at the acquisition date
over the vesting period. It was anticipated at 1 July 20X7 that 10% of staff would leave over the vesting period but
this was revised to 4% by 30 June 20X8. The fair value of each option at the grant date was $20. The share price
of Luploid Co at 30 June 20X8 was $32 and is anticipated to grow at a similar rate in the year ended 30 June
20X9.

ANSWER : The fair value of the replacement scheme at the grant date is $18 million (100 x 10,000 x 90% x $20). Since
$9 million has been allocated to the cost of the investment, the remaining $9 million should be treated as part of the post
combination remuneration package for the employees and measured in accordance with IFRS 2 Share-based Payment.
The fair value at the grant date of the share-based scheme should be expensed to profit or loss over the two-year vesting
period. Subsequent changes to the fair value of the shares are ignored.

my question : If the expectation was revised to 4% from 10%, why don’t we take the revised 4% ?

100 shares x 10,000 employees x $20 x 96% [new revised] = $ 19.2m

the rest of the question is fine when he deducts the amount already taken as part of cost of investment and divides it over the vesting period.

thanks