Music theory/Mode question
General mountain dulcimer or music discussions
You said: "B flat / G / F (melody string is F)"
In listening to your sound clip of your open strings, you have lowest string (bass) at Bb. The middle string is tuned to the G above the melody string's F. Thus, the highest sounding open string is the middle string G.
The youtube you copied below is playing Emma's waltz with a capo at fret one, resulting in the minor-sounding aeolian mode. This is what I guessed before with your tuning. On your open F melody string, the first fret of your melody string will be your 'home'/tonic note which would be a G (matching your open middle string in G). If you aren't using a capo (without telling us), you'd be playing the waltz in the G aeolian scale, in Aeolian mode which has a lonesome/sad feel. From the internet: "G Aeolian is the sixth mode of the Bb major scale · G Aeolian Scale Notes: G A Bb C D Eb F". Your tonic/home note is G, on the 1st fret of the melody string.
The reason your melody string is the F note LOWER than the middle string (usually it's higher than the middle string) is because if you tried to tune it to next f note one octave higher, at a 28"+ vsl that string would break no matter how thin a gauge you had. So you went with the F an octave lower which happened to be one note below the middle string G.
updated by @strumelia: 12/13/20 06:39:41PM

I'm also impressed that you figured out on your own so quickly how to get a sound clip up in your post.