All of the machines made in the last 6 - 7 years have sensors in them which detect the humidity, temperature, etc and adjust themselves to maximise efficiency. This will also vary the amount of water they use. Or at least that's what the manufacturers say.
That noise you hear is a result of you breathing deeply. Almost all machines will do the same if you breathe deeply. I'm sure it's no comfort to know that once you fall asleep, and your breathing falls into a nice regular rhythm, that noise will almost certainly stop. You could try not breathing so deeply (easier said than done I know). It is possible that if you increase your starting pressure a little you will feel like you are getting more air and you don't need to breathe so deeply. You may also have C-Flex turned on which will amplify the effect of which you speak. If this is the case you can try turning it off.
Those levels are lower than they should be. Unless you've been a heavy smoker for a few decades (or something similar), your oxygen saturation should be 90% or more. CPAP prevents your airway from collapsing, but if you are not breathing enough air in and out to keep you oxygen saturation up CPAP will not help. That's what BiPAP is for (or at least what it SHOULD be used for). It helps you breathe more air in and out with every breath, raising your oxygen levels and lowering your CO2.
Your throat absolutely can close while you are lying on your side. Some people only obstruct when they are on their back and, for them, avoiding lying on their back may be a sufficient treatment, although historically it is not very successful. However, it is not correct to suggest that your throat can't close while you are on your side. The majority of my patients obstruct while they are on their side.
I haven't been able to play with an F30 yet, but I can tell you from examining the pics available online that the elbow connectors appear to be identical, so it's hopeful.
Without an EEG recording there is no way to tell if you are asleep or what stage of sleep you are in. I'm guessing they use actigraphy to approximate that but it'd be pretty darn rough.
No, CPAP has no effect on narcolepsy.
That was easy.
Many people will never have an AHI of 1 or less. 3 or 4 will be as good as they will every get. If you feel much better and your AHI is 3 instead of 2, then go with it. Especially if your other medical parameters are good.
I wouldn't go that hot, or you'll be in the market for a new mask pretty quickly.
With home studies, a big factor is exactly what kind of equipment they used. Some home study sets only have 3 sensors in them, which leads to much less reliable data. Others have almost as much as a full in-lab study, so they are much more reliable.
One individual will experience some variation in their breathing from one night to the next, but all the data strongly suggests that it's pretty minor. Also remember the scientific rule of thumb - if you see a thing then it is there, but if you don't see it doesn't mean that it's not there, it just means you didn't see it. So, if you have a good quality sleep study with proper equipment and they record you having obstructive events, then there is little doubt that you do have OSA because there is an actual recording of it happening. If a study doesn't find anything, then it's always possible there is a problem and it just wasn't detected for some reason.
In my experience, home studies are more likely to over estimate AHI than under estimate it. It is certainly not the case that all of them use time in bed as opposed to total seep time. That is very much dependant on the specific system. Although most of my work is in a lab, I also use a home study setup regularly and it certainly uses total sleep time, as we record 4 channel of EEG to measure sleep stage, so we know when you are sleeping and we know when you're awake (we know if you've been bad or good so be good for goodness sake...).
Perhaps try to get a look at the original data, or have a second study and see how it compares.