i think i am having the same problem as the original poster but it's a little more extreme. I will try to explain my problem clearly

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When all my open strings are completely in tune the notes on my G string are not in tune with the rest. i have to play about 1cm (maybe a little less) closer to the nut to play notes in tune on the g string.
An example - Using a tuner to check the tuning I will play an in tune A on the E string (5th "fret"- sorry for using Electric bass terminology). I move directly across to the A string and play an in tune D. I move directly across to the D string and play an in tune G. Everything is fine until I move directly across to the 5th "Fret" and play a C. It is significantly sharp and I have to move my finger about 1cm towards the nut to get an in tune C. The tuning is affected this way pretty consistently the length of the string. I have been putting up with it lately but I am slowly going crazy.
I live in the Yukon and I am thousands of kms from the nearest bass repair. These are the things that I have tried to fix the problem myself.
1) re-aligned the feet of the bridge so that the bridge is further away from the nut on the G string than the E string creating a longer string length on the G to the E - I was hoping that this would move the note closer to where it should be but it made no noticeable difference except mess up my string height. i tried this at different string heights with no success. It is still sharp. i experimented with a few different alignments and the change was minimal.
2) I changed the g string. A friend had mentioned that he had had some tuning issues in spots on a string and they were fixed just by replacing the string which might have had some weak spots. This did not work in my case. The intonation problem still exists.
I don't think it is the nut height as my action is fairly low so I'm not bending the string much when I press it down.
I am at a loss to what is causing this. i hate having to shift my hand up a bit every time I move to the G string. My tuning is bad enough as it is.

Anyone have any ideas that I can try? I won't be seeing a luthier for a long time.