This is a good short video of Tissier doing irimi nage. The second half is in slow mo. Watch his feet. Watch his toes. And watch how at the end of the movement he even moves his core forward enough that the back left foot rises a bit off the ground. Leaving just the front right foot - with the big toe as the decoupler for his entire body. The timing of uke being released corresponds simultaneously with the draining of the energy into the ground from the front big toe. The energy of uke is drained through nage as well.
Even notice the two small irimi movements at 14-17 seconds. There's serious drainage going on all over the place. For anyone looking to "get this" idea of decoupling, even on an intellectual level, watch this video over and over.