I thought that all flats I tried, and I almost only play flats, were kind of not really fitting with the Stingray tone, at least not of my instrument, with active electronics and a maple board. The only thing that's been really nice on it has been balanced rounds, like Fodera nickels, Dunlop Nickels or TI superalloys. The LaBella Deep talking rounds were really sweet too for a great deep aggresive tone, but man I want to be able to play the bass too!
The ones I liked the most were TIs (not really doing it for me on that bass) and Fender CL flats (recorded beautifully but a bit hard to play despite good set-up), and both of them were kinda... strangling the sound of the bass, not matching somehow.
LaBellas worked but really worked against the Stingray inherent tone a lot IMO, and the GHS 35-95 I had on it were the same but a lot more choke-y on the tone.
The GHS flats to my ears, on all the basses I've tried them on, and despite the different gauges I've tried, have always had too much of the highs and clank of fender flats but with a different voice, and not enough of the deep, thuddy, woody sound that LaBella gives too my ears. I have yet to find a bass that they truly fit on, where their tonal attributes really shine and where another string would not have been more appropriate for the sound I'm looking for in that moment on that particuliar bass.
If I were you I'd try some new Cobalt flats, or the new Dunlop flats! I haven't tried those on my ray though, I imagine they would fit nicely. When I get my Sadowsky Blue Label 40-100 I might leave them on my ray for a while just to check how they fit.
Just my 2 cents, and we don't even use that currency!