I have a graduated 15ctw so its heavy at the bottom, but still flips. It's about 17 or 18inches I cant recall exactly. My shorter 2.15ctw, 14.5inch tennis necklace, same stone size all around, buttercup setting, actually flips a bit less and it doesn't bother me so much, it's kinda alluring how it moves with me. But bottom line, if the necklace is flexible it will likely move as you move, so flipping is almost inevitable. Maybe the shorter length helps the smaller one not flip as much.
I've tried testing out some options to stop the flipping. I may have a thin wire added to the side of the necklaces, not the underneath as some have tried. It will change the look a bit but add a rigidity that I think will help stop the flipping. Being less flexible is a trade off for staying stones upright. I haven't gone to see my jeweler yet tho, want to really think it over and try some at home remedies first. Hopefully my local jeweler will be able to make the alteration if I decide to go for it.
ETA: I may also shorten the graduated one, it's def always been too long on me. I think being shorter will help that one too.
Also adding, I've watched the flipping to determine the issue, from my assessment, bc the necklaces are flexible they act like chains and roll on my neck as I move. That's why I'm thinking adding the wire to make it less flexible should help. I read sodering links could help too, but for some reason I'm not keen on that idea. Will have to discuss with the jeweler if I decide to do anything.
Soldering the 7 or so larger stones together would help with either style. The flipping issue has to do with the type of setting, as well. My 11 ctw necklace was set in a heavy weight platinum setting so it didn't really flip.
Mine are both YG so makes sense that heavier platinum may outwiegh the stones and keep it upright more.
If anyone here has tried the soldering option I'd love to know how it worked out, and see pics how it looked after. Maybe just soldering the front part of each necklace would do the trick. If so, sounds like an easier and probably more cost efficient option.