With a lot of Bass guitars, and particularly Rickenbacker, the Bridge sits right on the end of the body therefore scale length is a very, very big deal. If the neck has been set too far south there may not be enough adjustment left in the bridge saddles, particularly A & low E, to intonate properly and this causes it to sound out of tune in various positions up and down the neck.
Here is a pic of mine to demonstrate just how far back things sit. Also worth noting where the 20th fret lines up on the body as a reference point but being a kit copy it may be slightly different.
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