Good advice, Alex. In fact, the shortest option is really tight (basically the space of a business card), so I’m a bit worried about it. Anyway, I also tried the 97mm + 20mm combo and it's fine — there’s no vignetting with the close-up lens (SMC-1) mounted on the flip. So this is probably the best option: fewer extension rings, less bulky setup... (until the proper port will be available)