Doing warmups is a great time to work on this, so is funakogi undo. In funakogi undo, when you drive your hips, you don't just want that motion to go forwards. Doing so makes the rear foot get light. You need to keep both feet heavy as you perform the motion. Part of that is how you drive the hips forward and back and how you involve the lower back. When driving the hips forward, the motion to drive the lower hips forward doesn't mean that you roll the hips forward with the lower back.
If you do, you will find that drives the motion upwards and makes the rear foot light. Also, I find that leaves my lower back fatigued rather than the hips. Instead drive them forwards by opening the hips. You will feel your legs want to open up too, but don't let them.
I'd like to quote this in another thread. For this particular thread, may I ask if funakogi undo
are done with hanmi
for your description?