I came home and picked out all keys I have for guitar work. The problem was that the thin e and b strings didn’t ring out well over the 12th fret. So I fixed a higher action on the 3 thinner strings. It became better, but not perfect. Then I started to play with a small amp, and suddenly I realize why it doesn’t work. A fretless guitar and bass has no frets (!!!), so your finger becomes the ”fret”. But it’s not metal, it’s soft tissue that lies over the string. A fretless bassplayer I know says he has the same problem on the g-string played high up on the neck. The string can not vibrate so much. For a guitar it becomes even worse, put your fat fleshy fingers on a thin string high up on the neck and it does not vibrate. One solution is to use slightly thicker strings. Another one; when you go over the 12th frets on the thin strings, put down your nails on the string and it sings better because it’s harder and more like a metal ”fret”. Tricky technique, but not impossible. Classical guitarists often use their nails.