You can modify the work quantity for a specific environment tile, such as mud, within the mod menu. I am looking to update the default value to make things a bit easier to use without tweaking, and will see about tweaking the work time for mud as that does make sense.

For spot size I prefer to keep it as is, as mainly this meant as a means of foraging having them be too small of a size would feel like its just farming.

Will there be an option in the future to change the forage size? Like the area pawns run to, to forage?

Not forage size, no.