Last attempt with this and adding other pendants…
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Hi! Since I am in this thread, I'll chime and share my thoughts if I may...
The tennis necklace is basically a thin line necklace... the same repeating pattern, like a "chain necklace with diamonds."
The 10 motif is a bold station necklace, so the two compete, especially when they overlap. My eye goes first to the 10 motif, and the tennis necklace is lost.
It seems like you are trying to stack your tennis necklace, so I'll assume the tennis necklace is the priority piece.
If you want to layer your tennis necklace, I think it works best with another line/chain necklace, or a pendant(s) "under" the tennis necklace.
Because the tennis necklace is so dainty, you really want it to be at the top. The eye will go there first and see it, and it will not get lost. Then, the eye will move down to see your other layered piece.
Since this is the VCA forum, I assume you want to layer it with something VCA. I would try a Magic pendant because it will land lower than your tennis necklace. Your tennis necklace lands a bit low (e.g. not choker length), and I assume you want it that length, but that is also the reason why you need a longer chain to wear below your tennis necklace.
Another thought if you want to stay with VCA and go all out on the neck and very casual, I would wear your tennis necklace with the 6 motif. The tennis necklace will be at the top, like a nice round choker, and it will frame the 6 motif.
Here is a visual... imagine the tennis necklace on top. You may have to adjust the lengths a bit, depending on where the 6 motif lands on you. The photo has the necklace worn high, but it will overlap with your tennis necklace as your tennis is long. I think you wil need to wear the 6 motif low. Basically, the look with the 6 motif is the "layered pendant" look under a tennis necklace. It just happens that all the motifs are VCA, so it's bold. If the lengths do not work, you can always just use other pendants.
If you don't like the "busy layered pendant" look, I would get a beautiful chain necklace and layer it. Now, you have a "chain necklace with diamonds" (e.g. tennis necklace) layered with another beautiful chain necklace. But... the tennis necklace needs to be the top necklace and stand on its own. Lots of beautiful chain necklaces now layered with tennis necklaces. I would personally do this and keep it a choker “chain necklace” theme and not do pendants.
Just my two cents. Hope this helps, and good luck!