I don't know where one begins to see issues with which corals, but I'm quite confident that a change of 0.2 dKH is not an issue for most organisms.
I'm not even sure that changes that happen every day within a day are even very important (say, 8 dKH dropping to 7 dKH then boosted to 8 dKH again the next morning).
I think most people that claim to have seen issues from lack of alk stability are referring to going for periods (days or longer) at one alkalinity then changing to a different alkalinity for another extended period, etc.
In that case, corals may keep changing the number of transporters needed to take up adequate bicarbonate, and may find themselves with too much or too little bicarbonate frequently.
But when that happens over the course of a single day, I'm not sure they are even responding to the minute by minute alkalinity, and may just average things out to get enough in a day. Adding or removing transporters from membranes is not typically something that happens fast, at least in the cases where I am familiar. It can take more than a day.
As evidence that this hypothesis may be valid, many people do once a day dosing of two part system, and I've not seen real evidence that their corals do not do just as well (albeit with more work) than people who dose alk with a dosing pump spread widely over the course of a day.
