Yep they could, in small realms.
Nope they could not, in large realms.
The vast majority of european kingdoms were more than a day's marsh in radius. The handful of exceptions doesn't make the rule.
As for the "not in large realms", which I suppose you mean kingdoms, I don't see why not. Regardless of how large their lands were, allies would, when marching, not be that far apart. The distance between their homes has no relation with the distance between their tents.
