You can't do this out of the gate. It is by default not proportional in size on the X & Y axis. This shape is way more about equal triangles than it is about radius of a sphere.
Look at the Width and Height properties when the object is at full scale.
Rotate about Z axis 17°
Look at the Width and Height properties when the object is at full scale again.
You might be thinking...
What If I rotate about Z axis 8.5°
now check your Z value and your line of thinking should get you the answer.
Once all your bounding box dimensions equal out, scale it up until it reaches 2.00, and the apply the scale.
Once you have done this, scale will represent the radius of your icosphere.