Enclose a gizmos icon in a Sphere Collider

As the title says, I don’t know if it’s possible.
In my editor I drag some sprites from the project folder into an Object field and instantiate them in the scene.
When I build the new gameobject I add a Sphere Collider.
When I hover the mouse over a game object, in Game View (always in edit mode), a drag icon appears. By clicking on the icon, which hides the Sphere Collider, I can move the object with the mouse.

The problem I can’t solve is how to set the radius of the Sphere Collider to the same size as the icon when creating the object.
The setting probably also depends on the size of the background image in Game View.
To complicate matters I work in both perspective and orthographics projection.

Do you have any suggestions to try working on?

For the moment I found a good solution in orthographic projection.
I set Size to one and adjusted the Sphere Collider to the size of the icon. By multiplying this constant by the size of the camera I always obtain the ideal radius.

I will now work on perspective projection.
Happy for any suggestions.