Here's a (the?) mysterious source of the story of a 38T 'glider mated to a 36T ring: 'tis me wot done it, sir! I did it ages back--surgically adapted me 38T 'glider to a 36T ring. Did it in August 2015 I did, and all these years later, it's still working.
Here's the story and the foto:
1) First, attached below is the foto of the violence surgical adaptation done to the 'glider. You'll see that the part covering the rear of the chainring has been removed. I could've left it intact, but the curvature of the 'glider would've been mismatched with that of the smaller ring, and I found that jarring to my sense of visual symmetry.
2) Why did I order a 38T 'glider when I had a 36T ring, you ask? I didn't: I started with a 17 x 38 setup on my Raven, and after a season and a half, decided to lower my gearing to 17 x 36. This has worked very well for me. The summer after the change (2016), I did a 2400 km trip in the Rocky Mtns and Cascadia, and the new gearing did the business.
3) Consequences of the fit of a smaller ring, and the surgical change? WRT the smaller ring, there's more play (I often use the word "slop"), both fore-and-aft and up-and-down. I sometimes run the bike sans 'glider, and honestly, I can't tell the difference betw the "with" and the "without". (Then again, maybe a bloke that uses a word like "slop" isn't a good judge anyway.)
WRT to dirt, nothing extra that I can see. The only place I ever see any slight buildup of oily crud is on the entry and exit "gates" of the rear part of the 'glider where it embraces the rear sprocket. I clean that away once or twice a year, and I did that before I changed the size of the ring and made the adaptation to the 'glider. I don't ride a lot in the rain, but I do ride about 10% of my distance on rural gravel.
4) There's more surgery, however, that you can't see. This is subtle, but in my opinion, it's at least as good as the surgical adaptation you can see. The 'ring you see in the photo is a Surly stainless item. I have used three of these, the 38T item which was the original, dating from spring 2014; and two 36T rings, which I used until 2018. Then, I ran into problems with new stainless rings being both oval and out-of-plane, so I was getting a major tight spot and a variable chainline with two successive new rings.
I decided to switch away from the very durable stainless rings to a beautiful alloy item made by Origin8 and sold by Rivendell Bike Works. This is fractionally thicker than the Surly stainless ring, but is perfectly round and flat. Its toothed section is, however, 3mm thick, and this is the max recommended by Hebie.
So, I did another surgical adaptation on the remaining part of the 'glider which touched the new ring, thus: On the inner part of the 'glider where it touches the front, top and bottom of the chainring, there's a small collar of plastic, about 1 mm in size, on both inner and outer parts of the 'glider. I carefully removed that with an exacto knife and file, and -- voilá! -- more slop play right where I needed it. My precious alloy ring doesn't get squished/polished by my equally precious adapted 'glider. Each remains at a suitable mechanical distance from the other, a very COVIDian fix that predates 2020 (Dunno what the collar did -- add some rigidity, perhaps?)
So there we are: my bit of heresy seems to have brought me no mechanical misfortune, so far at least.