It's a variation on the theme, called "foot on floor".
I'm lucky enough to not get true dp, those crazy unexplained 3am to 7am rises, but I can guarantee like clockwork that on most work days, as soon as I get up and just move around a bit, then over a period of 30 mins to 60 mins, I'll go up by 3 or 5 or more.
I knew that already to an extent from bg testing, but libre has let me watch it more carefully, and let me fine tune it a lot so that I'll get a sense of whether fof is kicking in, and, if so, how hard, and then I can generally pin it with, for me, 2 units or so.
Just makes things a lot tidier for when I come up for lunch - that 3 to 5 unpinned rise would easily take me well out of range, but pinning it keeps me in range coming up for lunch so I'm not having to do corrections at lunch - I've already corrected before it's happened by not letting the fof get too mad by doing the 2u by predicting from past experience and libre corroboration that fof is likely to happen, so have stopped it.
That's just how it works for me, not at all suggesting the same will be the case for your kid, but just something to think about.
The basis of fof is probably just that it makes sense from our genes from caveman days for our bodies to have more sugar kicking around as soon as we get up, but in a modern T1 context when we're not fighting sabre tooth tigers that often, maybe not so much. Still might be useful getting a place on the tram or tube, though...