Need some helpful advice on fret markers

I have been building stringed musical instruments since 1976.  I was building dulcimers before 6 1/2 and 13 1/2 became a "thing".  I was going to attend a festival in Lancaster, Pa when the Pandemic put a hold on everything.  I made 6 dulcimers and had to go back and add the new frets on some of them and I was also informed the fret position markers were not in the correct place. Here is my question: I have 6 more I am making for the return of the festival in July. I am using a 26" scale and I have incorporated the 61/2 and 13 1/2 on the fingerboards.  I am not sure where to place the fret position markers..I have been all over the interne looking at pictures.  Any advice would be great.                                  .                     

I have posted pics of the ones I am making now and the ones I previously made.