OK, I will add back more soil. I know what you mean about 'mum knows best', which is why I left it rather than rush around looking for an incubator. It is just so hard imagining a little turtle hatching then crawling through 10 inches of soil!
Another Ornate owner mentioned that the middle/south US box turtles eggs are a bit harder than the box turtle eggs along the Eastern coast. And that the mother often pees around the eggs to add extra moisture. The egg is well packed into the soil to keep it stable. And I am not even sure, there could be more than one, I stopped when I found the one egg to avoid disturbing it.
She did such a good job, and it was so cute watching her disguise the site; ruffling up the leaves with her back legs.
I managed to get temps to about 29/30c by raising the tub up an inch on wood slats and putting a heating pad set on low on the floor, beneath it (not touching the tub), along with maintaining the black light above. It is nice to have the probe right by the egg, so I know exactly that the temp is at the egg.
Fingers crossed, but at least Fiona is happy again!