Hy Hassan,
In nature I have seen them in sandy places. I think they have rain all year round, but flowering and activating with early-mid summer rains.
I have seen them deeper than yours. About 10 cm. deep.
The sandy soil looks dry little after the rains end.
Good luck!
Do you know the colour of your bulbs?
Here are some pictures for you to enjoy!
You can see clearly the substrate in pic 0450.