I'd say smaller.

I have cedar lattice for trellises and they cannot wrap around the lattice very well. They need something smaller to grip properly.

I break off dozens of stems every year trying to tuck them into the lattice.

My next trellises will be cedar framed with wire livestock fencing in between rather than lattice.

This photo was taken in a garden with over 100 Clematis and they used this fencing for every one.

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here it is covering the cedar fence:

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unfortunately, I learned this after my DH built me a ton of lattice fences and trellises for them to climb....

Taken at the Rogerson Clematis Collection:

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Thank you!
The actual cedar pieces will only be 1" x 3/4"... same size local nurseries sell for clematis. You don't think it will work? I've grown lots of clematis at other houses before but always IN another plant (rose bushes mainly) or up string.

Well, now that I think about it, the clematis in question was previously growing on a wood trellis that I took down.. it was the fan-shaped type made out of wide wood slats. it seemed to do OK on that, by twining to itself as it grew...

OK... so it looks like the proper thing is wire... but, aethetically, I don't want to use that :( This is a VERY visible architectural detail on the house. It's a focus both from the street (long view) and up close, since it's beside the walkway. And since I'm in Maine, this will be a mostly-bare structure for more than half the year. So it's gotta look nice :)

Maybe I need to plant something else with the existing clematis, to give it some structure to climb... or transplant the clematis elsewhere. There isn't enough room for a climbing rose, though, since it's RIGHT next to the walkway. Anything planted there cannot protrude off the garage wall more than 12-18", nor be prickly.

I have Clems on wooden fan trellises too and I do have to tie them up. They don't climb it on their own or stay woven into it. They don't break as easily though as they do when I try to weave them through lattice.

Your experience may be different, others have success with chicken wire and I don't and am removing it.

I found out about the livestock fence long after all these other supports had been in place.....