We encounter this frequently in certain Northwest Washington DC neighborhoods--the mini master bath. It's just big enough to do what you need to do -one at a time- and no more. This is the lay out that comes with the typical 40's built colonial. Three bedrooms up with one half of the second floor allocated to a front to back master bedroom. Located at the rear of the master is one closet --not large enough to store clothing for two. Next to the miniature closet is the infamous mini master bathroom. Neither is big enough. Most people find this irritating.
How do we get a bigger bathroom without building an addition? Interior reconfiguration. In this project in progress we are combining the area once occupied by closet and bath to get a reasonably sized bathroom. We created new closets at the other end of the bedroom.
When we are done it still won't be a BIG bath--but it will most certainly be big enough to function very well. It will probably look a lot better, too. We'll return to this project when it is completed.