trying to unscramble your post----
- it is a good idea to keep
tanks above 30% -- the tank works on a vacuum seal, and when it gets low the vacuum gets wonky (flooding)
-yes egos/evod and other regulated devices have a X second cuttoff, as you said to keep damage from occuring to your
tanks.(if no cuttoff was active and you held your button down, it would evaporate all your liquid and continue to heat up untill your plastic melts or any other damage... and continue to keep putting power.)
-the decrease in TH could be a number of factors unrelated, but to stay on this subject - you may be "over pulling" on your tank and it is "flooding". i notice when a tank starts flooding, you get less TH and less vapor and it will continue to decrease as the flooding gets worse. - try puffing slower/less power(ecigs are not the same as a real cig and you do not "hit" them the same)
any one else feel the need to correct me or add any input - your more then welcome to