Sheldon's (may he rest in peace) chainline specs for double and triple cranksets all quote values for the middle position that results from mounting the crankset on the manufacturer's recommended bb length. On a triple this means the figure Sheldon gives is for the middle ring, and on a double this means the figure will be for a plane right in between the two rings. This means you will have to do a little fourth grade math to figure out what the chainline will be on the ring position you are planning to run. From there, if you need to get closer, you can use a different size bb spindle than the one that the manufacturer recommended for multi geared applications. If you do this before buying your cranks and bb, you'll get something that will probably work on the 1st try.