Randy,
Is this an open air rack, similar to the ones on my DIY page, or a solid top rack like one built with melamine? If it is the open air rack, I just bend my heat panels slightly up or down to adjust them for proper fit. If it is a melamine type rack, I cut a spacer prior to starting that is the correct height for the shelf, and insert the spacer between each shelf prior to screwing in the next shelf. This allows you to have the proper, exact spacing for every shelf.