This is only correct for the 2nd UC payment onward. For the first payment, having the full £609.05 deducted effectively erases the majority of that 2 week run on payment, which was a bonus payment. Those who were claiming IR ESA with no CB claim received an extra 2 weeks payment during the month they migrated over (to help tide them over during the 5 week wait), whereas those with part CB ESA received exactly what they receive every month.
