I think you should go fishing… Not being crass, just so you can make a real-world observation.
Use the largest round bobber you can find. Now, run a line down from that bobber and start adding weights until you get that 2/3s submerged, like your illustration, then watch how it behaves in the waves. Watch, particularly, how the stem moves. It will tend to rotate and wobble around an off-center point, just as the earth does. part of that is due to the different layers of wave action, working on the surface. I do not have the science behind it, but I have been fishing, off and on, for some 45+ years, and am offering an observation, that I’ve noticed, ever since I was a little boy, learning to fish, on a river-bank, beside my granddad.
Part of the significance of the line and weight is stability, including the same stability of depth of structure, at least to some limited degree, but that wobble and rotation are going to be a problem. You’ll be closer to your solution, when you can eliminate that wobble. Part of the solution is to use some ballast in the base of the sphere, with the rest suspended beneath, just like a hook and sinker, for fishing., but using a partially weighted bobber.
If there’s an issue with heaving, you can add heave-plates. I hope that helps, at least toward some real-world experimentation. Heck, load a beach-ball with the equivalent ballast, of sand. Ball has x amount of buoyancy, sand weighs y. Bigger the demo, the better, just maintain your preferred 2/3-3/4 submerged attitude, and see what you can adjust, to make it work…
IMHO, the spherical floating city isn’t going to work, but that’s my opinion. I’ll leave it at that, until proven, one way or the other.