This is something I've had a lot of problems with. I understand the benefit of small diffs, but I can't seem to find a way to really apply this for any actually meaningful changes. In my experience I would spend some time coming up with a system of multiple abstractions that are interdependent and then getting single logical commit for proof of concept would require hundreds of lines. Splitting the abstractions into separate commits would be confusing so I don't think that's good. Maybe I should stub functions a lot more aggressively and truly aim for minimal. The other problem is when you are replacing an abstraction in an already large code base, the raw number of changes required could easily be in the hundreds or even thousands of lines.
I have had the same experience. I work on a number of large C++ codebases at work and often times I just can't find a way to break most things up into small diffs.