Not to be in contrediction with others, but just to give you another point of view
( maybey I'm just lucky with the way it goes in my enclosure )
The ground is covered with a fine layer of eco-earth and there's two big plants in the enclosure. It's been her third cluth this year and she always did choose the nest box ( eco-earth and peat moss ). She usually starts ''diging'' one or two days before she will lay her eggs ...
The only answer I have, it's probably easier to lay her eggs in the nest box than in the plants ( you also have to consider if the soil of the plant is near dry or moist, cause she will choose the best site to lay ... )
Martin 
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1.1.3 rhaco. ciliatus
1.1.2 P.M. grandis