Your statement is correct if you were talking about heating up a glass tank where most of the heat produced at the bottom would escape before it made it to the top... Plastic is a much better insulator than glass and it holds the heat in the tub... Heat produced at the bottom then rises to the top... I know this statement is incorrect bc I put an accurite at the top of one of my tubs and then one in a small tub (not sure what size but it was about 6inchs tall like yours) ... After an hour of the heat pad running both temps were the same (difference of a couple tenths of a degree)...

You say its wasted space... How so if theyre using it?? I go into my snake room every night and my snakes are climbing all over the place so I wouldnt say its wasted. You probably have never seen this because your snakes dont have the option to move around much... As far as your percentages my snakes sleep all day and are out and about pretty much all night so its probably closer to 60/40... Again its probably harder for you to tell when your snakes are actually awake and about since your tubs are much smaller...

To me personally its wrong to keep a pet (My snakes are pets first and breeders 2nd) in what I consider to be a small environment just so you can justify having more of them.