On various sites, there's been much discussion of the placement of the fretlines on an Ashbory, and the accuracy thereof, and as a new Ashbory owner (and bass player, both fretted and fretless, for over 20 years), I finally feel qualified to chip in.
When fretless basses have fretline markers, those markers are exactly where the frets would be, and the dots are therefore between the frets. To play these in tune, you fret the string directly over the fretlines.
When fretless basses have no fretline markers, the dots are usually placed where the fretlines would be. So you fret the strings over the dots to play in tune.
An Ashbory is set up like a fretless bass with fretline markers. So one would assume that you fret on the fretlines to play in tune. However, many people have observed that these fret markers must be set up inaccurately, since you generally have to fret in between them, rather than on them, to play in tune. It's my belief, on the other hand, that the fretlines are indeed marked accurately - the issue here is that the strings are so thick that they actually come into contact with the fretboard somewhat further up the neck, rather than directly under the finger. So, on the E and A especially, you do need to fret slightly further back (i.e. between the frets) to compensate for this.
It's a tricky business and I'm still getting to grips with it. But the bottom line is that, as others have said, you need to let your ears guide you!
K.