This sounds like the ol' "how much foam do I need for THIS cup?" dilemma.
with a smaller diameter opening, you need less foam to get that foam "canvas" on which to float your rosetta.
With a larger diameter opening, the physics is on your side, but it takes more foam, or more time to get an adequate foam "canvas" on which to work.
Honestly, though, once you get used to the basics, and once you get a feel for cup size in proportion to foam needed, it's not difficult to pound 'em out fairly consistently.
Still, though, the most beautiful rosettas I've poured have been in 6oz. bowl-shaped cups that I got from JonR10 a couple of years (or more?) ago. (thanks again, Jon!)
When I was still working bar on a regular basis, I got so used to pouring into to-go cups, that when presented with a "latte art bowl", it was an instant failure. I just got so used to having a smaller diameter opening, thus, requiring less foam, that when presented with a vessel theoretically intended to be conducive to such practice, the surface area was so large that the foam I made just wasn't enough to get that proverbial "canvas" under the crema, and it resulted in something sort of resembling art. It was enough to impress some, but it was barely there at all.
Owner - AJ Coffee Company