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Those RotoSounds would absolutely NOT be MY choice of string for ANY short scale bass.
I only suggested them because the poster to whom I was replying wanted that gauge range.
To be clear, I do not, for a short scale bass.
What you described is nothing more nor less than what a string which has too little tension will do - it will flop around and be inconsistent in pitch, no matter how good all of the other factors about the instrument are.
For the life of me, I have no idea what drugs the engineers took, who first suggested that strings for shorter scale instruments ought to be lighter than for long scale, be it a bass or anything else.
MOST STRING MANUFACTURERS HAVE IT WRONG !
What I personally would suggest for a short scale bass is a whole step HEAVIER, in order to recover the tension lost when comparing it to a long scale bass.
So, these are the changes which might make sense :
If the G on a 34" bass was .045" in diameter, then on a 30" bass, it should be more like .051" to maintain the same tension (if the 'unit weight' remains the same, IOW, the core diameter and how the wraps are done internally).
If the D in a properly balanced set was 60 in long scale, then for short it should be 68, given the same considerations about the build of the string.
If the A in a properly balanced set was 80 in long scale, then for short it should be 91.
If the E in a properly balanced set was 106 in long scale, then for short it should be 120.
The above gauge numbers are based upon the premise that for a string of a given diameter and internal construction, the active portion of the string is 1.133 times the length on a 34" scale bass that it would be on a 30" scale bass.
If you tune it to the same pitch on the shorter scale bass without changing the gauge nor construction of the string, then the tension will be 1/1.133 of what it would be on the long scale bass.
If you want the tension not to be reduced on the short scale bass while keeping the same pitch, then you must increase (multiply) the diameter of the string by the ratio of the scale lengths of the two basses, in this instance, by 1.133, to get the required diameter for the short scale bass.
This is what I did in the above examples.
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BTW, a good example of a set which has properly balanced tension from string to string is the GHS Balanced Nickels.
Even so, the only short scale version of those has gauges from 44 thru 106, but it is still heavier than a 40-95-ish set.
Anybody who likes roundwound bass strings [and has a long or a short scale bass] ought to consider trying GHS Balanced Nickels.
Unfortunately, there are less bass string choices in general for folks who prefer flats, or anything else not roundwound, such as me.
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Yep, I have GHS Balanced Nickel Shorty's on my Mini and they sound fantastic. I highly recommend them. Unless someone else comes out with something new that will be better than the BN's they will be the only strings I use for the Mini P. After I put them on my Mini I picked up a long scale set for my Fender Flea Jazz Bass and I am equally impressed to say the least. I love flats but these BN's sound superb. GHS hit it out of the park with these strings But as always, YMMV. Cheers.