It looks a simple question, but it needs a lot of technical comments to answer.
In Rhino, nothing is 0, the smallest value in 0.001. It is the document tolerance. For that reason, you sample doesn't work, becuase is:
1 + 0.001 + 1, is bigger than 2! Then, there is not space to place both rectangles.
By other hand, there is a value of Distance tolerance in Nesting Parameters:
You must reduce this value to 0.005 in your sample. As more precision, more time needs to be calculate.
Your smaller distance between objects will be between 0.001 to 0.005mm.
If you have any doubt, don't hesitate to contact me.
Thanks and best regards,
Rafael del Molino
TDM Solutions SL