Probably the 2 mm difference does not matter. If any flex occurs, the seatpost below the shim will still contact the wall of the seat tube and add some support. I think as long as your shimmed seat post is inserted past the minimum insertion mark you are safe. Part of the idea may be to not have a lot of exposed seat post, making a long lever arm with lots more force on the seat tube/top tube, seat stay area. I am not a mechanical engineer and I have not stayed in a Holiday Inn Express, so these are just my guesses.