I do not think there may be one reference. Every design is different and each time you need to find the best solution and it is not always the best technically because economics demands its own considerations. It may be big difference depends on where do you use your SIR in filter, in antenna or somewhere else; how many of resonators are used and what is the coupling. Good solution may be found only as results of thorough analyzes of all the requirements and possibilities and seeing the whole project. I used SIR a few times for filters and always feed it with microstrip lines and feeding point was in the middle of resonator, so the structure was symmetrical. Now I am considering it for antenna, but so far it is just an idea, no design done yet. For the references you can use well known books from David Pozar, Brian Wadell’s Transmission line Handbook (but be careful: there are a lot of typos). On this site there are a lot of topics about references for microwave design books, please check them by search. For me it is not so easy to give you references because I usually use kind of unusual way to find information. For many years I developed thousands of detailed worksheets and they help me a lot. When I need to find more information I use my electronic library (it is really huge) and do the search by keywords. Then print those pages that related to my project and put them into special folder. This is proven method but as result I do not remember the exact titles and authors names for all these books. The only drawback is search time that sometimes may be as long as 20 or 24 hours, then it may take a few hours to print and sort related pages. This allows to have good and easily accessible information for the duration of current project.