I am using the
You have to make sure that the radius you allow the sprites to be placed in is less than the extents of the plane and the half the size of the sprite. because when you place the sprite on the edge of the radius, the center of it is on the borders of the plane, so half of it is outside it. Did I understand the problem correctly?
As for the relation, the
bounds.extents describes half the size of the sprite in units, while
transform.localscale is the scale relative to the object's parent's scale. It is also an indication of the current size compared to the original size of the sprite, it doesn't indicate the size in units.
So assuming the parent's scale is 1:
bounds.extents = (original bounds.extents) * transform.localScale