UC & ESA deduction - Is there a discrepancy or am I missing something?

I recently wrote a query on my UC journal as follows, 'I was wondering if you could clarify something for me regarding the deduction for ESA, please. On my payment statements it says that my monthy payment is reduced by the ESA payment, which I understand. However, I am confused by the amount deducted each month:

'As this is an average of other benefits that you're continuing to claim

Employment and Support Allowance minus ‑ £609.05 '

I receive two ESA payments of £281.10 each calendar month, the first on or around 14th of the month and the second on or around 30th, a total of £562.20 pcm. This is less than the £609.05 per month deducted from my Universal Credit each month and has been applied to each of my payments.

I would be very grateful if you could explain the workings as to why the deduction is significantly higher than the actual amount of ESA received.'

I subsequently received this reply from the UC centre, 'ESA is calculated every 2 weeks however universal credit is calculated monthly. As some months have more/less than 4 weeks (ESA) we need to calculate a monthly figure which explains this.

We take your ESA payment X 52 weeks and ,/. by 12 months.'

I am still confused as I never receive more than the two payments stated per month and still cannot understand the discrepancy between the amount deducted and the actual amount of ESA I receive. I apologise if this is a stupid question, but it appears that the total amount of the deducted discrepancy amounts to a 13th month of ESA. Wouldn't it be more transparent and accurate to deduct the amount of ESA I actually receive?