* Her distance measurement is extremely sensitive. Basically, whenever your character's model does any animation, that counts. Literally your character standing still registers as movement, since it is still doing animations. While the distance from that alone is tiny and therefore does not recover a relevant amount of Nightsoul points, it still means that you get the 1/s bonus from her A1, even if your character is literally just standing there.
* Switching characters also registers as movement. The distance this registers as seems to vary a lot though, and also depends on what animation you were in before the switch. If you switch out while Iansan is still finishing her attack animation, that allows you to "carry over" some distance to the next character and therefore count (since obviously Iansan's own movement does not count). The amount of this is generally very low and therefore probably not really relevant though (I got between 0.05 and 0.6 Nightsoul points from it, depending on what character I was switching into, animation state and god knows what else - obviously measuring with the switched-to character standing completely still).
* This should be clear from the text of A1, but just to clarify: The Nightsoul-consumption based bonus of 4 you can get at most every 2.8s also counts for Iansan herself if she is the active character. Since she will be on-field consuming Nightsoul points right after you activate her stuff before you switch to your next character, that means you always get that 4 bonus at least once.
* Burst animations also count as movement. For how much depends on how much the actual character model moves during the animation, of course.
