The eggs were laid on the vertical, smooth side of the arch toward the back of the tank. I believe they chose that location partly due to its privacy from nosy people like me. The koi angels are much shyer than Lindsay and Stevie.
If all goes well, the eggs will hatch within another day or two and the parents will place them elsewhere on the arch or on the leaves nearby, where they'll dangle by their heads until they are strong enough to pop off and swim.
Since this is the first time they've gotten this far without predators in the tank, they might not be completely successful at raising new angels the first time around. But it's been my experience that if I leave them in this tank, they will continue to try every couple of weeks until they master the art of sex and parenting.