The higher temp is gonna cause thicker vapor not matter if its sativa or indica.
Your post confuses me cause you say
"I see a good low temp sativa cloud rolling up the tube of my vape bong, my lungs absorb almost all of it in a short time"
then
"I have trouble seeing the cloud through the glass because it isn't quite as dense. Then after a full 20 seconds of holding my breath, on exhale there is still a huge amount of visible vapor!"
So when you see vapor in your bong, you exhale nothing, but when you dont see vapor in the bong, u exhale a big cloud?
Also, THC and CBD are in both sativa and indicas, its the ratio of these two that give you different effects. Sativas are generally lower in CBD whereas indicas are higher in CBD.
Next time you vape, during the lower temp hits when you cant see vapor, blow your hit into a flashlight and I bet you that you will see your hit.