On a normal working day sitting at a desk, I'll take 20u of fiasp for breakfast and maybe a few more u later on. That lets me eat a few biscuits during the day.
On a pottering around day, mending things, packing, stuff like that, I'll take 13u and probably need to eat.
On an active day (walking, cycling, whatever), I'll take 8u and need to eat a fair amount during the day.
So yes, variation due to activity seems entirely normal to me. And it's why I don't let people tell me that carb counting is the be all and end all of sugar management, because exercise is a much bigger thing.
I change my fast acting insulin to match what I'm doing, and if I'm active I'll take the excuse to eat with it.