I believe I follow your situation but, yes, a photo would clear matters for me. If I understand correctly, your posts sit proud (in front of) the deck skirting.

Probably the easiest solution is to build framing to fit between each post, then attach the lattice and install.

I took a slightly different approach for ours as the construction is different by attaching the framing to the post face whereas you will need to do so from the back.

Lattice is not sufficiently sturdy to install without a frame and cutting it can be a challenge too, that's why I built what you see here.

{{!gwi}}

Thank you for responding. Here is a picture showing the set up.

What about attaching the lattice to the back side of the joists? That will look a lot cleaner from the front, as you won't see the cut edges along the top. You'll still have to cut around the beam, but it will be less noticeable.

That was an idea I had and agree it would look better. It would just be hard to get under there to screw it in. There's only about 26" of clearance under there but it's doable.

No need to use screws. Use a nail gun and make short (if a bit awkward) work of it.

And if you want to hide the post/beam, just put a bush or large plant in front of it.

Yes, your photo shows the issue. I agree with weedyacres, install from behind. Then, accent the protruding joists by designing a corbel to fit over them, or just a decorative end cap.