OK. Three personal experiences with short scale strings:
1) La Bella 760FL. Yes, the E string can get a little thumpy, but overall it is the least thumpy over time of the "old school" flats. My friend had a set which I helped him get used, and the E string never completely thumped out. Yes, old school, but a good old school, with good articulation and tone. I would put them on my shorty, but for #3 below. I do have them on my mid scale Jaguar H which turned it into a veritable mid-scale funk machine.
2) First alternative. Not really a flat, but La Bella 60-115 nylon tape. They are a different mellow than flats, but a good mellow. Underneath the tape they are essentially as set of 45-100 conventional rounds, so they don't get thumpy, either. If you are wanting to get away from "old school," the white tapes are marginally brighter than the blacks. I gigged a set of whites for two years of constant gigging before the frets finally wore divots into the nylon and rendered intonation insecure. But they never lost their tone since the nylon wrap keeps finger gunk from killing the strings. You may have to adjust the nut slots to fit the strings. It's been awhile since I have mounted a set, so I bought a set to go along with purchased parts for a frankenbass that is my upcoming winter mid-scale project bass.
3) And now for something completely different and my favorite: GHS Balanced Nickels round wound on a round core. The set on my shorty travel bass has been on the bass for two week-long annual trips to Mexico with my party band and are still going strong. Wait - there's more. Being rounds, the E string doesn't get thumpy. With the round core, the G string is not twangy. They are consistent string-to-string and up the neck. They last a long, long time. Reasonable price. Big, round tone. They are not edgy like NPS rounds can be. Nickel is more dense than NPS, so there is more tension than with NPS of the same gauge. Over time, they mellow to a woody goodness reminiscent of "golden era" Fender flats, but still modern tone.
To my hands, all three of these sets have adequate tension and feel: not too tight, not too rubber-band-y. Each set has great consistent tone for its respective genre. By definition, a shorty is about two frets shorter than a regular long scale bass, so any string set will feel like tuning a conventional long scale bass with the same or similar gauge strings down to D-standard then capo the second fret. The physics simply preclude a really stiff E string.
I have to comment about a couple of recommendations above: neither Fender Flats nor Ernie Ball Cobalt Flats come in short scale. If Fender Flats came in mid scale, I would play them. I love their modern growl. I gigged a set of regular long scale 9050CL (no longer offered) on my custom P-style fanned fret bass for two years. When the E string started to thump, I bought a single 105 Ernie Ball stainless steel flat and gigged the set for another year. But the Mustang to the contrary notwithstanding, you really do risk breakage both from the tight bend over the bridge saddle with the string-through-body, and the tight wrap of the E string speaking part around the tuner post. So I can't in good conscience recommend them for a short scale bass, although the tone and feel are superlative on regular long scale basses. Likewise, I can't recommend DR nor Dunlop: DR, although they may have short scale back in production, start dark, get darker, and darker, and darker, and from the initial post, it appears that's what is being avoided. Likewise, cost. I just can't justify the cost of the Dunlop when there are other lesser expensive, and to my ears, better sounding strings out there. YMMV.
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