I don't have the Super Jig18, but ....

Are you able to move the two boards so they are at 90 degrees to each other and flush along the top? It matters not where along the jig they are located at first, only that they be 90 degrees and flush.

Then move the two boards in unison towards the left against the left front side stop or as close as you can get

Then move the left plastic front side stop to meet the front board.

It doesn't have to move very far, I'd be surprised if you would need to move that stop more than a 1/16th of an inch.

That's the way I read the instructions, Tom.

The top board is just a spacer--all the work is done from the front of the jig on the front board (the top board is simply a spacer) and the finger template is rotated for pins and tails and the board you are working on is likewise switched out. This is different than any other dovetail jig, many of which cut pins and tails (top and bottom boards) at one time and the top and bottom boards offset. The Leigh jig uses two different set ups (hence the necessity for two different routers, two different guide bushings, and two different bits).

Give that a try and post your results. I've used a lot of jigs, and Leigh is the best (although not the easiest to use).