Design or Sound

Calling All Luthier's and MD Players of many different dulcimers;

Because I am enjoying my discovery of my MD, I have been noticing differences in fret boards, some are floating or braced up or placed flat on the sound board and some have sound holes in them.

Is this a design preferance? OR

Is it a way to get a certain sound from the instrument?

Thanks for your generous and enriching information.