Flat side to the material for me. So much easier to clean and I can see from the vapor path that it makes a more even distribution. With the material actually in the basket it seems to funnel the air to the center.
Speaking of even baking. One thing I've been trying recently with pretty good results is packing the stem as normal and dropping a Dynavap CCD on top of the herb. This is admittedly VERY FIDDLY but not terrible since I use it almost exclusively through water (upside down so the CCD doesn't fall out). The herb gets very evenly cooked without much stirring at pretty high temps.
The SONG is really smart BTW (thanks for adding it to my order free of charge when I mentioned my previous GONG cracked!). My main gripe about the GONG was the screen was nigh-impossible to install flat end up. Having a non-tapered glass tube makes it so I can just slide it in from the other end like with the stems.
One thing I'd love to see is a slightly longer stem on the SONG so you can see the vapor production before it goes into the water piece. But maybe I'm the only one who judges their draws visually like this. A longer stem could also leave room for a carb hole, a very welcome feature for high volume water pieces that have a tendency to blow the load back up and out (the ABV confetti cannon).
And yes... Some day I'll get this dang LED fixed. But this device has been life-changing for me and I refuse to be without it for even a day, much less however long it would take to get it fixed.