Create the blended surface using a tolerance when exact tangency is not possible.
<= Tolerance
Define the angular tolerance for blending the surface. A tolerance is required when there is not enough distance between the two surfaces in which curvature can be created. A common circumstance occurs when the edges of the surfaces touch.
Exact
This option uses the tangency of the surfaces selected.
Ruled
This creates a flat/ruled surface between two surface edges.