Apparent 18% reduction in benefits after transition from ESA to UC

Hello, I'm wondering if I''m misunderstanding the information I've been given in my UC statement which arrived on Saturday.

I have been on Contribution related ESA.
I was/am in the Limited capability for work and work-related activity group.
I was receiving a Severe Disability payment.
I am in receipt of PIP (which I know is unaffected by my migration so I'll leave that out of the equation)..

Prior to the application process I was receiving £1325.65 a month in Housing benefit.
Plus, £972.60 in ESA/Severe Dissability payments per month.

So a total of £2298.25 per month.

The statement says I will receive £1,439.97 towards my rent, so a little improvement there.

It then says I will receive a standard single person's allowance of £400.14 per month.

Limited capability for work and work-related activity allowance of £423.27 p/m.

And lastly £232.79 p/m in transitional protection.

My total therefore prior to deductions is £2,496.17

It then says they will take off £609.05 in deductions as this is an average of other benefits that you're continuing to claim (ESA).

Leaving a total payment this month of £1887.12

If I'm understanding correctly his means I'm £411.13 worse off after migration. A reduction of almost 18% in total benefits excluding PIP.

Can this be right? I've no idea how I can survive on a reduction of over £400 a month.

It's essentially th money I spend on food and travel expenses.

Please can anyone advise.

Thanks in advance.