This is mostly right, but it’s more a range of potential grades a refinery is set up for, but you can get to those grades by blending, in which case it could be

This is mostly right, but it’s more a range of potential grades a refinery is set up for, but you can get to those grades by blending, in which case it could be cheaper to buy a heavy and light cargo to get to a medium grade than buy a medium grade cargo…