How should you think about new wall framing on a subfloor with allowance for movement?

[octomore]

I am building a music room with an extra acoustically insulated wall on one side, where I now want to add an extra layer of mineral wool in front of the existing fiberglass wool shown in the attached images. The horizontal studs in the image are part of the new framing.

Something that struck me while working with the first horizontal studs is how to think about fastening and placement since they stand on an existing (glued + screwed) subfloor that has a 10mm movement allowance against the existing wall's framing (see detail image). What I want to avoid is mounting the new framing in a way that causes significant tension and, in the worst case, failure if the subfloor swells and moves. The room is 9m long, and what we see in the image is one end of it.

My thoughts are therefore on which of the following is most correct:

• Move the horizontal studs out 10mm so they align with the edge of the subfloor, i.e., the entire new wall framing would have a 10mm gap against the existing wall, just like the subfloor?
• Allow the new studs to sit flush against the existing framing but only screw into the subfloor so that the new wall does not connect the subfloor and existing framing?
• Screw the new studs only to the existing wall so that the floor can move under the new framing?
• Fasten the studs to both the floor and the existing studs

I am tying myself into knots in my reasoning about this because I simultaneously think the subfloor should be able to move slightly but also that the new framing must be held firmly in place. The new framing also means screwing the outer studs into the existing floor, walls, ceiling, and each other, which also directly means that the floor is connected to both sidewalls.

Then I wonder how much the subfloor actually swells or moves when it's fastened with glue and hundreds of screws along the entire beam structure.

Maybe I am complicating this much more than necessary...