Sometimes when the mask is leaking high but AHI is normal may be during a time that you are not having as many events but it is an average of the overall night. While leak is important and ResMed machines do compensate for the leak better than most, what it cannot do is compensate for your positions during sleep. If you are on an Auto there will always be a time where there are more events in order to find the optimal pressure within the algorithm. If you go to your back and you have more events (or other positional increases) this will show in the scores but your leak may indeed be perfect. If there is a way that your DME can find what your average ending pressure is, and switch to normal BiPAP at that pressure. You will probably find that whatever pressure is ending you at 1.1 is going to continue to keep you at that AHI. I did this with my CPAP and as a result I always start and end at 18.0 with no ramp and no fluctuations. I am generally coming in around .5 AHI every night.
The Transcend is also very popular, and I believe a lot less expensive than either of the two mentioned above. You probably can do without the humidifier for the time you are gone. I rarely use humidification myself and I have been using CPAP as long as you! The transcend is the size of a soda can and is perfect for air travel.
Clear airway (or central apneas) are where you technically do stop breathing for a spell, as opposed to Obstructive apneas which are caused by your airway closing off. Hypopneas are partial obstructions which are not completely closed, but closed enough to cause your oxygen to drop and/or wake you up.
It sounds like they are using deadspace treatment on you, where they use a non-vented mask and a specific length of hose to force you to rebreathe your exhaled CO2 in order to stimulate the breathing response during the central apneas (the theory being that the body has a CO2 threshold that forces us to take a breath of O2.) It works but people can and do find it uncomfortable. It also needs to be set up and monitored by a qualified technologist in order to make sure it is safe and effective.
sleeptech is correct that ASV (adaptive servo ventilation) is the general standard for treating central or complex sleep apnea. The way ASV works is it monitors your breathing for the first 20 or so minutes and calculates an algorithm which forces the air into your lungs during the times where you have a central apnea. essentially breathing for you. I have seen it work wonders in patients with Hypocapnia, Renal Failure, Congestive Heart Failure and COPD where Central Apneas are quite common in patients. However, your doctor would need to determine if your ejection fraction is above 45 before undergoing a titration in order to ensure its safety.
Hope this helps.
P.S. 3.9 is a normal AHI. so the treatment is working by most evaluations.
Are you sure you are on BiPAP and not an AutoPAP or an AutoBiPAP? People on AutoPAP have to go through several apneas/hypopneas before they get to an optimal pressure. Some people (myself included) cannot tolerate the sleep onset apneas and it makes getting to sleep very hard. It is quite common with people with severe apnea, but other people can have it too. What also happens is if the pressure range is set too low it can keep your AHI higher because it is not hitting the correct pressure settings. Some AutoPAP prescribing docs will put a pressure range of 4-20cm H2O or 4-15cm H2O but others set it lower and it can also cause problems. The statement that BiPAP is not for treating OSA is not 100% accurate. In patients were expiratory pressure is intolerable it works wonderfully so comfort is often a deciding factor as to whether to switch, the presence of emergent centrals is also another deciding factor, followed by ASV in the presence of unresolvable central apneas. Respiratory failure we generally do not treat in the sleep lab.
My advice would be to ask your doctor or medical equipment company what you are using, explain to them the issues you are having and see if they can come up with a solution. "I've gone through two sleep doctors who one, never heard of it, and the other one doesn't know what to do about it." Not sure where you are in the world, but there needs to be a sleep doc that can answer you or do something for you to help. You said you turned off your ramp, this is a start. But I suspect you need to start at and stay at your optimal pressure to keep your airway from collapsing at the start of your sleep. To do this you need to get an attended titration study, with a qualified sleep technologist, to monitor your titration and get you to an optimal state. Even people with a 15.9 AHI can require well over 20/16 cm H2O to keep their airways open.
My advice would be to research reviews of masks that are on the market today. From what it sounds like to me, the mask you use may not be right for your specific "facial landscape" . There should be a mask out there for you however, it just may take some trial and error. NO one should have to be in pain from an ill-fitting mask