TDS on Bonus received during middle of year

Example:

Say estimated annual net taxable salary income at beginning of FY 2021-2022 is Rs 20 lakh

So projected tax comes to 412500

(Keeping aside CESS for ease of numbers)

So employer deducts 412500 divided by 12 as monthly TDS = 34375 every month

Now say in month June Bonus 15L is declared and received also.

So now total annual tax liability would be 412500 + 450000 = 862500

Balance tax for 10 months = 862500 – (34375*2) = 793750

So monthly tds deduction from June end should be = 793750 / 10 = 793750 per month

BUT employer has deducted very high amount which is little more than 30% of Bonus amount in June 2021 itself?

Why? Can anyone explain Pls.