Do you have the new-style rack, as shown here?
New #1 Rack
DM, thanks for the reply. No, I do not have the new one. But I don't think it solves the issue as is. Mine has three slots, top, middle, bottom. The spacing between the bottom and middle is 3 5/8". The spacing from the middle shelf to the inside top of the SI#1 is 7 1/2". Assuming that I want to leave at least 1" free space at the top to prevent the vent hole from being blocked, that gives me a middle shelf to top effective height of 6 1/2". I could make these two headspaces about the same if there was a middle shelf slot about 1 1/2" above the current slot.
The new rails you mention have an additional slot, but it is below the middle slot, not above. Just looking at the picture, it seems that the original three slots are in the same position relative to the hanging hole, with the new slot but equally in between the lower and middle. If the new slot was above the middle one rather than below it, I think we'd be in business.
Just now typing this, an idea came to me idea based on paidin's message above where he mentioned drilling the vertical part of the rail assembly. How about I just flip the new rails upside down, and drill new hanger holes in the appropriate location. Then my new shelf slot is above the middle, not below it. But drilling that hole in the right location may not be that easy as the now top slot is in the location where the hole would be.
Hmmmmn, I need to think this through a bit more but maybe this can work out. Of course the ideal situation would be a new rail assembly with slots added both above and below the middle slot for a total of 5 slots. I would buy that in a heartbeat.