The concept of flow should bring to mind an image of the water in a river inexorably making it's way to the sea. Nothing is required to make it flow. It just does. The natural state of the water in the river is that it is going to flow to the sea. All anyone can do is stop it, slow it down or divert it. The river wants to flow.
So don't manage flow. Flow doesn't need managing. Flow only needs enabling (if it needs anything at all).
Enabling the flow of a river would be to remove the rocks which impede the water, to open the sluice gate, to widen the waterways, to remove the meanders and so on. Enabling flow would be to remove the barriers to flow (or perhaps to be gravity). Which is exactly why conventional managers struggle to improve patient flow...
The job of a conventional manager is not to remove barriers but rather to introduce them and then to manage the consequences. Policies, rules, criteria, budgets, targets, utilisation, standards, SOPs, reward and punishment schemes, job descriptions, service specifications, objectives, 'the plan', 'the contract', blah, blah, blah. The list goes on literally ad nauseum. These things are not managing flow because flow does not need to be managed. Worse though is that it is these things themselves which are the impediments to the natural flow that wants to happen. They are the rocks in the river. It is because of these things that patient flow is more like a sputtering tap than a flowing river. To put that another way, it is because of management that the system does not flow. You can't manage flow.