Just a quick update. At the start, I mentioned I was getting faded patches. I'm blaming this on not having the transfer on super tight. It wasn't so much of an issue before with the mug presses, since they clamp the transfer tighter. I also reject mugs which have little dents or rippled coating, so this has eliminated any patchy printing.
Transfers are cut up to the height of the mug, I haven't noticed any gas staining.
All 10oz mugs, regardless of quantity, including enamel mugs and aluminium water bottles are put in at 20 mins at 160 degrees as previously mentioned.