Peek the Geek

Okay, I'm gonna try my best to describe this. I apologize if this gets confusing.

I had a bike fitting done today at a Minnesota bike shop. Among other things, it was decided I would need a shorter stem, so the shop guy takes the old one off and starts to put the new one on. An important detail here is that I have a 1" steerer tube and 1" headset, and the stems are Ritchey WCS 1 1/8" inch stems that come with shims for using the stems on 1" steerers. Like other shims I've seen, these have a lip around the perimeter of one end.

So, the shop guy proceeds to install the stem with the lip of the shim underneath the stem. Then he says, "You can't use the top cap you're using with this because the top cap is 1" and only presses down on the shim---not the stem itself." (Can you picture what I'm describing?) "You need to use a 1 1/8" top cap."

So I say, it's my understanding that the lip of the shim goes above the stem, so that the top cap presses down on the shim, which in turn presses down on the stem.

Shop Guy: "No, the lip goes underneath."

Me: "But I had it the other way, and it worked fine."

Shop Guy: "No you didn't. The lip was on this side of the stem when you brought it in."

Me: "Yes, but you flipped the stem to an upward angle. It was angled downward when I came in."

Shop Guy: "No it wasn't."

Me: "Yes it was."

Shop Guy: "No it wasn't."

Me: "Okay, fine. Put it on your way with a 1 1/8" top cap. Just make sure I get my 1" to take with me."

So.... How should the shim be installed? With the lip on top and the 1" top cap that came with the headset? Or with the lip on the bottom and a 1 1/8" top cap he had laying around? (And if the lip goes on the bottom, why the hell is it there in the first place?)

Thanks for reading.