A question concerning extra frets on diatonic dulcimer

Hello everybody,

my dulcimer has only a diatonic fretboard since I didn't insisted on adding the extra frets when I get it from the luthier. Otherwise it's a fine instrument.

Now I tried to get the tones by pressing the strings between frets 6 and 7. But I didn't get it. It stayed at the tone of fret 7 or six depending where I tried. I also tried to use a capo to get it. Same result. Am i missing something? I thought the frets are just for indicating the position to press the strings but otherwise it should work as well without them (so in theory the whole fretboard could be empty if I somehow would know where to press the strings).

I assume I got something wrong, what's it?

And: Is there a way to "emulate" the extra frets without adding them?  E.g. by wires and glue?

The luthier which build my dulcimer lives more than 600 miles away so I can't go and let him fix it. And as far I know there are no dulcimer makers nearby.
Other luthiers are but I'm not sure whether a guy, who usually builds and fixes guitars or violins actually have the skills for getting it right on a dulcimer.

Thanks and best regards from Germany, Jost.