The only spot at Pacific Dunes where I can even imagine an infinity green (which would also be skyline) is #3. Tom Doak, did that ever enter your mind?
Sheep Ranch is certainly full of them.
That's because the routings are fundamentally different.
At The Sheep Ranch, and on certain holes at Bandon Dunes before it, a number of holes are oriented to play with the ocean as their backdrop. Mr. Keiser liked these holes because you got a view of the ocean ["it's an ocean hole"] but you never had to worry about hitting a shot over the cliff.
For Pacific Dunes, I wanted to use the cliff edge as a hazard . . . my standard was not how many holes looked at the ocean, but on how many shots the ocean was in play. You can hit the ball over the edge six times: twice on 4, once on 10 and 11, and twice on 13. But I did have the advantage that the inland property was BEAUTIFUL, so people were less bothered by not being right on the edge of the cliff all day.
With regard to your question about the third hole, that green had the two little dunes at the back of it from the time we first saw it. As we lowered the green some to make the approach less intimidating, the dunes behind got bigger in relation to the green, and felt like more of a backstop. But we liked the peek between them toward the ocean and #13. If we'd actually gone to a green with no backstop, I think it would have been too intimidating for the approach, and I don't think Mr. Keiser would have liked that. And the green was never going to profile against the ocean, since the shot was always going to be uphill.
Note that I am not totally against building an infinity green; I've done it numerous times. There aren't many that are more dramatic than the 12th hole at Cape Kidnappers, and to a lesser degree, the 15th and 10th. At the 10th and 12th there, though, the green is backed up to the point that going over may result in real trouble. Most infinity greens are sheep in wolves' clothing.