Not really. That really breaks the idea that you first find the team that is the Constraint in the Work Flow, and then focus on the step/stage/phase/column of that team that is the Constraint in the Work Process (of that team).
The portfolio has one constraint, the Constraint in the Work Flow. It might change, yes, but due primarily to the Work Load. You need to look at the Virtual Queues that build up in front of the teams. In a simplified mode, you can count the Work Items and pick the one with the longest queue. A more refined way is to use probabilistic forecasting - for each team - and see which team would need the most time to process its virtual queue.
(Note: these queues are “virtual” because their items have not been released into the work flow yet; they have not been “committed” to.)
Great question, which often leads to the “Aha!” moment of learning about the TameFlow Approach.
Let’s use the 3J metaphor.
So you have these squadrons of Jeeps (Teams) that need to reach the base camp at the other side of the Jungle (the end of the Portfolio Backlog). They will take different paths or Journeys (the different Virtual Queues or backlogs in front of each Team) through the Jungle (Work Flow).
One of these Jeeps will face the most challenging Journey: it has to climb a very steep mountain. We can foresee that it will be the one that will need the most time (Constraint in the Work Flow), so we will make sure to focus on keep it going at the best of its capacity, keeping it moving at its maximum sustainable pace (by focusing on the Constraint in the Work Process). All other Jeeps can take it easier, because they are faster and have plenty of capacity to catch up.
Now in this swarm of Jeeps that are traversing the Jungle - and they all have to bring their cargo (Deliverable) to the same base camp before sunset (Deadline) - just as there is a Jeep that we can foretell will be the slowest one – under “common” / normal conditions – all other Jeeps will move faster than that one and get to base camp before the Herbie Jeep. Again, note well: under “common” / normal conditions (Common Cause Variation)
As we know, when we traverse a Jungle, well, “things happen.” So we might have the fastest Jeep on the least challenging Journey of all that will encounter Mr. Murphy. And that fast and favored Jeep will have to stop. The stoppage could be so sever that – under these “special” conditions (Special Cause Variation) - that it might end up becoming the last Jeep heading toward the base camp.
This unlucky Jeep is Constraint in the Work Execution. This Constraint came about not because of what we can foresee (the Work Load / Work Flow) or what we know (the Work Process) but because of the “stuff that happens” factor, courtesy by Mr. Murphy. Since this stuff happens during the Execution of the work/plan/portfolio, we call that Jeep - which is experiencing the bad luck - the Constraint in the Work Execution.
And if there are multiple Jeeps all encountering Mr. Murphy on their way, then the one that is delayed most will be considered as the Constraint in the Work Execution. The other ones can recover at their convenience… they are still ahead of Herbie notwithstanding their meeting Mr. Murphy.
We need to have prompt signals - during Work Execution - that some Jeep is encountering this stuff. That’s why we have Buffer Management and in particular the Bubble Fever Chart. For an animated example of this see at the end of the Visual Portfolio Management blog post. Do you literally see how the Herbie team is represented by that purple bubble? Give this kind of chart to the steering committees and portfolio managers and they will be very, very grateful. But, of course, in order to get there you need to implement all the things described in the book; and for a deeper explanation see Chapter 20 - Operational Governance in PEST Environments of Tame your Work Flow.
Hope that makes it clear!