Yes, the US 9 created a far better drape! But I'd suggest using the largest needle possible. Swatch first. Get a nice drape without it being holey or lopsided looking garter stitches.
However, I can't claim credit for the idea of using the 9. I read up on all the other Mara Shawls over at Ravelry. If you click Projects under the Mara Shawl, then click YARN IDEAS....well, I spotted several Malabrigo Merino knitters. One of them generously included helpful notes. She mentioned that she started out with a smaller before, but frogged the entire thing at some point and started over with the US9 for better drape.
So I followed her lead!
I'm knitting a black Mara Shawl right now, using Ella Rae's "Latte" yarn. It looks and feels almost like Malabrigo Merino, but it is heavier. Prolly heavy worsted. Anyway, I'm using a US 10.5 for it! It's creating fabulous stitches, wonderful drape. Plus, I'm sailing through it. It won't take as long to reach that 46" width goal! Yay for that!
The black Mara is for me. I'd have kept the cream Mara if my daughter didn't like it. But she LOVES IT.
Ella Rae Latte is 30% alpaca, 30% milk, 40% microfiber (whatever that is). It's a real soft single ply, so it pills if you even look at it wrong. Good yarn for a shawl rather than a cardigan, which is what I originally bought it for.