First of all, I'm going to preface this by saying that this is completely hypothetical, and there's a reason I generally draw and RP Katja as being far, far below this line: because they're just way more into acting on a human scale. They prefer being at least non-huge enough that they can actually see people, and generally like being at sizes where they can actuallyโฆ hang out with people! Hold them! Hug them! [REDACTED]! However,
Basically, by scaling the average time it takes for motor signals to get from the brain to a human's feet, and multiplying that by the speed of light (for, say, fibre-optic nerves), the highest height you could get about the same performance at is ~8,600km.
Now, seeing as Katja's radius of being able to do Reality Hacksโข is equal to the square of their height in metres, that's a radius of about 7.4ร1013m โ about 495AU, or 68 light-hours.
I think a good upper limit to put on them is probably "they haven't figured out how the hell to make FTL communication systems actually work with the degree of parallelism or precision that a nervous system requires, and they are unlikely to ever try". That, and Doing Not Magic over such an immense area that it takes nearly three days for any resultant light or radio transmissions to reach them is both boring and nerve-wracking for them, a being who, regardless of their power, still has the mind of a mortal and a deep aversion to accidentally ruining anyone's day or worse.
