session map testing so far indicates little need to reposition to be closer to the heater, at least with mine. I see no appreciable difference in performance between 12 and 24mm, given the same load, and prefer the deeper bowl which makes for spill free stirring.
My results differ a little. I loaded three stems with .o7 g each of the same material, lightly packed. One was with an elbow screen, which left the top of the load 2-3 mm from the heater screen. The other two had Zion screens adjusted so the top of the load was 12 mm and 24 mm from the heater screen. I set the power at 50%. I pre-heated each hit for 12 seconds, then drew for 10 seconds attempting to keep a consistent rate. At 24 mm and 12 mm, I agree that the difference is not significant. At 2 mm, however, I clearly get more and thicker vapour. So there does seem to be a drop-off as you move back, but it isn't linear.
It's also not significant. Your heater and mine aren't the same, and I'm not sure what will actually get put into production. It really doesn't matter for the same reason the load distance doesn't matter: you can always find a combination that works for you. As long as there is a power setting that can reach combustion for your load distance, you can find something.
For the record, at 100% power, 20 seconds pre-heat, and huffing like crazy, I could not make a load 36 mm away from the screen do anything but taste horrible. At 24 mm I got thick heavy vapour and almost a burnt taste but not quite. At 20 mm I got a cherry. 20 mm is pretty deep, so I think the Zion has enough range to satisfy everyone.
I notice more clogging the lower the temperature. I really don't seem to clog the mouthpiece screen that often... Beta testers have you experienced much clogging?
Not really. I examine the screen after every load and if I think it is starting to get clogged, I give it a quick ISO soak. A lot depends on your material. When I was testing ultra fine grind, I had to watch for clogging.
The ones I HATE are any that are difficult to seat correctly or that shift around in use.
I feel the same and sadly, glass parts aren't perfectly uniform so in some stems the Zion screens will behave like this. ELBs and elbow screens won't, of course. I wouldn't expect this to be a common problem, and
@RastaBuddhaTao has said he'll look into improving this aspect.