For quite a while I had a fretless 4 with a 34" scale made by one company and a fretted 5 or 6 string with 35" scale made by somebody else. The necks were different and so was the string spacing. Playing fretless in tune always seemed to be more difficult that it should be. I recently have been lucky enough to get fretted and fretless 6 string basses that are for the most part, the same basses in terms of scale length, neck, etc. (F bass BN6 and F bass Alain Caron 6). I have realized, in only a short time with this situation, that my fretless playing has significantly improved and become much more enjoyable. I would highly recommend to anyone playing fretted and fretless basses to try to have two identical basses because the consistency between the two is a great thing.