@dedicated-dad I knew what you meant and second @Dusty-Turtle on joining the 4 Equidistant Strings group.  We're happy to have you here at FOTMD!  

Yes, "upper strings" meaning higher tones, treble, higher register.  The strings nearest your body when playing.  

It seemed to me the OP was referring to the strings closest to the body as "upper strings" of the equidistant strings because he clearly asked whether they were played together as if they were close together (as some melody strings are doubled).

"Upper" strings???  No such thing.  Dulcimers are not vertical instruments! 

Do you mean the strings closer to you than farther away?  Or higher pitched versus lower pitched? Or melody versus middle drone versus bass strings?

As Skip says, there is no "proper" tuning or a 3, 4, 5 or 6 string dulcimer; just a number of possibilities depending on the  kind of music you want to play and how you want to play it.

Like most everything else with a MD, there is not a 'proper' tuning for 4 equidistant, it depends on what you're trying to do. The strings are equally spaced across the nut/bridge, like a 4 string banjo, so they can be picked individually. This layout is used primarily for fingerpicking/flatpicking

Hey @Dedicated-DAD, first you should know that there is a whole group here dedicated to 4 equidistant strings .  YOu might consider joining, perusing the old conversations and perhaps starting a new one.

There are a number of ways people tune for 4 equidistant strings. Some just add another in the same pattern, so they might tune DADA.  Janita Baker tunes something like D Bb A D.  That gives her a chromatic scale, enabling her to play blues and ragtime and jazz. But she only fingerpicks, never strumming across all strings.  I recently learned that Neal Hellman often tunes DAdd.  Those two high D notes are not played together, but rather he plays in a drone style in that tuning and gets an extra high D drone that way.

I'm sure there are other variations, too. All of them equally "proper."  Again, I urge you to joint the 4-Equidistant Strings group and pursue your interests there where you'll find more expertise.

What is the proper tuning configuration for a 4 equidistant string dulcimer?  Are the two upper strings played together, as if they were close together?  Thanks.